Ian how true, we don't want knee jerk reactions, what we need is Federal money, as in the Hawke Govt days when they built the mighty Burdekin Falls Dam in North Queensland, while we are at it we could use some extra Howard money to put hyrdo electric power stations on all suitable dams, so that we have complimentry power, or is that too sensible, logical and so should go to a committee.

Toowoomba City Council was promised $46M of Federal and Queensland Governments money ($23M each) for its proposed water recycling plant. Both Governments accepted the Council’s rejection of rainwater tanks as an option for the region’s future water supply. The Council estimated that rainwater tanks fitted to existing houses in Toowoomba would cost $5,000 and yield 25KL from 9KL of storage capacity. Neither the Federal or Queensland Governments questioned the Council’s data.

In reality, the cost of supplying, installing and plumbing (including with pressure pump) a 5KL rainwater system for an average house in Toowoomba is under $3,000 provided all houses are supplied to achieve cost-reducing economies of scale.

In the 12 months to 30 June 2006, there was 603mm of rainfall in Toowoomba. This would have yielded 59KL of water for an average Toowoomba house with 150M roof area, collection from all downpipes and use of rainwater for hot water, laundry, toilet flushing and outdoors. A 5KL system would have overflowed by about 29KL during extreme rainfall events. As part of the plumbing package, an automatic switching valve is installed for returning the household to mains water the instant the tanks run dry, and back to tank at the next rain event.

The reason why rainwater tanks are not a significant source of water supply in Toowoomba is because Queensland Government policy throughout the 20th century was to discourage them. 29% of non-capital city households in Queensland have rainwater tanks but only 5% in Brisbane.

Now, the State Government wants all new houses in Queensland to use rainwater tanks. The Government considers that installing rainwater tanks in existing houses is too expensive and therefore the law only applies to new houses and major renovations.

However, if all houses were required to reduce mains drinking water consumption by 40% at point of sale, with rainwater tanks deemed to comply, there would be a significant drop in the cost of installing rainwater tanks in new houses. All house owners – new and existing – would benefit.

The Federal and Queensland Governments do not express an opinion on this proposition.

Greg Cameron

I think the main theme of the article is sensible and that there will be an impact if councils strictly adhere to the rainwater tanks requirement.

It would be interesting to redo the calculations with some less optimistic assumptions. When you say most councils is that 51% of councils representing 51% of the potential new residents? When you say that they must have a tank does that mean that a 1000 Litre tank will suffice to meet council requirements or must they have a 13,500 Litre tank? Is it always true that a resident who collects 13,500 Litres uses all the 13,500 Litres before he uses mains water or does he sometimes just prefer to use mains water for cooking and washing and let the tank water be used for flushing the toilets and watering the garden. Does the council requirement extend to apartments and townhomes where they don't have space for a big tank or sometimes any tank at all?

Is there any data on reduction in mains water usage after the start of the rainwater tank requirement? If these regulations have been in for a few years it would be interesting to see how much impact on the total water usage they have had.

Editors - In future please use ML for MegaLitres not Ml. It is much easier to interpret.
19.5 ML/day – 2.015 ML/day = 19.45 ML/day not 19.35 ML/day. It doesn’t make any difference to the general argument, but its good to add up correctly.

The Australian Bureau of Statistics has collected and published detailed data on an estimated 24.9 million megalitres of water consumed in Australia in 2000-01:

• Agriculture accounted for 67 per cent

• Households nine per cent

• Water supply, sewerage and drainage services industry seven per cent

• Electricity and gas generation industry (excluding hydroelectricity) seven per cent

• Manufacturing industry four per cent

• Mining industry two per cent

• Other industries three per cent

Water Tanks may well help the 9% of water used by households but will do very little for the legitimate needs of agriculture. This article does not address the major problem.

Greg,
If I could afford a rainwater tank I would fit the largest one possible for urban useage, however if the government made it mandatory, I would have to sell myself sexually to get the required income, a prospect I wouldn't look forward to.

Not everyone is in the financial position to install rainwater tanks even though they would love to do so. We all pay tax, even we pensioners pay G.S.T.in a critical situation on the driest continent on Earth with the Howard Government having a $10.8 billion budget surplus, is it not a reasonable request that it either build dams, as Hawke did, or subsidise to a large extent rain water tanks, for those who are prepared to install but have no cash up front?

The key point is that most, if not all councils are mandating water tanks and when faced with this mandate, the builders are going for maximum benefit to maximise the marketing advantage.

The average house now has 250m2 of roof area so 600mm in Toowoomba will equal 150,000L of captured water.

So the key point stands. The market for mains water is already shrinking but new long term supply infrastructure is being justified on the basis of an expanding demand. And this will destroy the economics of even the existing infrastructure.

ericc-

Under Part 25 of the Queensland Development Code, the acceptable solution for rainwater tanks is a follows:

“(a) i. The rainwater tank has a minimum capacity specified by the local government; or
ii. where the local government has not specified a minimum capacity, a storage capacity of at least 3000 litres where used for external use only, or 5000 litres where used for external internal use.
(b) The rainwater tank must be installed in such a way that it receives the rainfall from a roof catchment area of at least 50 square meters.
(c) Where rainwater tank water is required to be used internally, it is connected to all toilet cisterns and to washing machine cold taps.”

http://www.lgp.qld.gov.au/docs/building_codes/queensland_development_code/referencedInLeg/QDC_Part25.pdf

QDC Newsflash dated 18 August 2006 states “The Australian Standards allow Councils to refuse to authorise cross connection between a rainwater supply and a town water supply. Where this is the case, it should be possible to plumb rainwater separately into the house.”

AS3500 is the Applied provisions of the Standard Plumbing and Drainage Regulation 2003. AS3500 provides the deemed to comply methods for plumbing of rainwater tanks. Where a person meets the requirements of AS3500 the Local Council may not refuse plumbing approval.

http://www.lgp.qld.gov.au/docs/corporate/publications/building_codes/newsflash/2006/NewsFlash241.pdf

The Newsflash also says “the Australian Standards do not prohibit the use of rainwater as drinking water.”

AS3500 provides acceptable solutions for plumbing a rainwater supply to the drinking water supply. AS3500 does not control the use of rainwater. Water collected from roofs for rainwater tanks is not owned by the State in Queensland. A person has the legal right to use rainwater for drinking water supply. The plumbing must comply with AS3500. Rainwater that is connected to the mains drinking water supply is drinking water for plumbing purposes. The owner of the rainwater – the householder – is responsible for its quality.

The Queensland Government would have householders believe that the State Government controls their rights to use rainwater. The State does not have this right. The State regulates construction, installation, plumbing and health aspects of rainwater tanks, but not the use.

Greg Cameron

As I've indicated elsewhere, I think the author's costing assumptions are somewhat on the optimistic side. That aside the calculations appear to stack up in the case where

a) The roof is of median size (or greater),

b) household water usage is average,

c) all household water usage comes from the tank except when it is empty, and

d) the installation costs are as as low as they can be.

But what of the houses of less than median roof size? That makes the optimum tank size lower, but smaller tanks cost more per litre of storage, which pushes up the net cost of water.

The same is true if the household water usage is below average.

Some people will not want to drink or shower in rainwater, which again implies a lower optimum tank size, and higher net cost.

The costings calculation requires that the 13,500 litres consist of a single tank, because two tanks of half the size cost more than one tank. Tanks of that size are usually round, but in any case rectangular tanks cost more.

A typical 13,500 litre tank occupies 7 square metres of land. No everywhere has a 7 square metre patch of level land, so extra work may be required to build a suitable foundation. Again that increases the cost. It may also be impossible to man-handle such a tank into place because of obstacles, requiring the use of a crane. More cost.

Taking all those considerations into account, what proportion of households could really make economical use of a rainwater tank? What about the rest? Should they be condemned to install uneconomic water tanks, or live with perpetual water restrictions?

BTW, installing a large tank on my property appears to be impossible without demolishing the house and car port. There is no mobile crane available with sufficient reach.

Sylvia.

for those who may be depressed about water, as I was becomming. Can I suggest a thorough reading of this site

http://www.abc.net.au/news/newsitems/200608/s1720514.htm

I'm not saying Aussie is leaking in the same manner as Mexico, but suggesting the manner of thinking of the problem, so evident in Australia.

The suggestion to me was if we were consious of our use of this "right we have to water" perhaps problem solved?

I'm seventy five and remember well padlocks on tanks, children were barred from access, just in case. All water for personel use was in a shallow bowl early morning. The same water all that was available for 24hrs, the exception of course was for drinking, kept in a galvanised bucket. This in the mallee of WA.

When I consider my present use of water, I'm ashamed.
While I'm much more conscious than most I know, I feel as though I had lost some part of me? this site reminded me of the loss.

I never felt deprived all that time ago, I'm pleased to be reminded.

Maybe the thinking could also be applied to "history"
There could be a problem, what if everyone had the temerity to have their own history? Too radical of course, I'd fail any exam anyway, memory is so unreliable! This may also fail to recognise myths and fairytales can have histories, that ain't science?

Whew glad to get rid of all that

fluff

FLUFF,
You are an inspiration to all, I laughed a couple of years ago when "new thinkers" came up with the "new" idea of rainwater tanks. It's like the Top 40 these days, if you bother to listen occasionally, you recognise some of the words, the "new thinkers" have used the 1960's songs, and put a different "beat" to them, so very creative. I hope to see more contributions from you on this and other subjects.
Regards, Shaun.

Thats a bit of a mixed bag, Sylvia. The stuff about the crane is fine but most of the tanks will be in new dwellings remember? So they can be put in first, under the slab if desired or just buried before the landscaping starts. In any event, they can be done when the machinery is already on site and for a fraction of the cost of a retrofit.

The other points about variations in cost due to roof size, use and tanks size are relevant but just barely. The modelling found that unit costs per KL varied only by about ten cents/KL. And the proportion that may or may not be used as drinking water is very minimal compared to the remainder of normal use.

And even in retrofits, empty tanks are very light. In fact, the biggest problem with empty tanks is with sudden gusts of wind that can shift them about.

And wrt one of your earlier posts, these costings also take into account the cost of buying mains water if the tank runs dry. This produces an average cost/KL of all water so the increased use of mains water when a smaller tank is used is reflected in the average cost to the household. I think this is a truer and fairer view of the real cost structure than the simple calculation of tank water alone. And as the prices of mains water increases in future to cover the excess capacity, this averaging of costs will really show up the folly of a less than optimum tank size.

The proportion of Australian households that could make economic use of rainwater tanks is a minimum 75%. In the 2001 Census, occupied private dwellings in Australia were 5,327,309 separate houses (75.3%), 632,176 semi detached, row or terrace houses and townhouses (8.9%), 923,139 flats, units or apartments (13.1%) and 134,274 other dwellings (1.9%).

It is straightforward to calculate the cost effectiveness of rainwater tanks for people who do not live in separate houses. A cut-off point could be determined, if required.

Based on 175m roof area for a separate house, the actual yield from a 5KL system is around 75KL for the 80% of Australians who live within 50KM of the coast.

The incentive to maximise use of rainwater (which the householder owns) is to require reduced consumption of mains water (which the State owns). People actually drink 1% of purchased mains drinking water. Maximum yield of rainwater is when it is used for hot water, laundry, toilet flushing and limited outdoors. People can choose to use water saving devices if they don’t want to maximise rainwater use.

A simple solution to the problem of tank size (in existing houses where engineering solutions for large tanks may not be a viable option) is to have numerous small tanks linked in series. Since maximum yield is obtained by ensuring that water is collected from all downpipes, whereby 100% of the roof area is utilised for collection, 1KL tanks are a solution because they neatly beneath the eave of a dwelling and any number can be installed. Small tanks no more than 800mm wide do not impede movement. And with demand from 5.5 million separate houses, watch the rainwater tank industry develop innovative sizes, shapes and colours to meet consumer tastes.

The Victorian Government estimates that rainwater tanks in every house in Melbourne would yield 60,000 ML a year (toilet flushing and laundry cold water use only), cost less than $950 million and would be water bill neutral.
Source: Sustainable Water Strategy Central Region Appendix 2 page 144
http://www.dse.vic.gov.au/DSE/wcmn202.nsf/LinkView/427BD3FAB0838556CA25709F00148870DEE554DEB21669DBCA256FFE00103BF8

Greg Cameron

The size of the urban house is getting bigger thus bigger water catchment area for that water tank. The rains will come, and too much for some and your water prices will likely go up because councils will not be raking in as much dollars as earlier when consumption goes down.

Thankyou Fluff, for your thoughtful contribution. We live in a very 'throw-away' society today it seems. No thought of anything outside our immediate needs or wants. I feel Australia has become a self-indulgent and ignorant nation.

It was announced today that the Porters Creek Wetland Stormwater Harvesting project on the Central Coast of NSW will receive Australian Government funding of $2.6 million toward a $16 million investment. The project is intended to allow additional extractions of up to 5.4 gigalitres from the Wyong River for the region’s drinking water supply.

In March of this year, the Australian Government announced funding of $6.61 million from the Australian Government Water Fund towards the $37.76 million construction of a pipeline to enable water transfers between the Gosford-Wyong and Hunter regions.

The Prime Minister, Mr Howard, today congratulated the Wyong Shire Council for “its commitment to finding innovative water solutions to major water management challenges”.

It is noteworthy that Wyong Council does not consider that rainwater collected from roofs for rainwater tanks by all houses is an innovative solution - indeed it is not considered to be a solution at all.

Rainfall as recorded at the Gosford BOM measuring station was 804MM for the 12 months to 30 June. This rain was sufficient to provide 93KL of water for an average Central Coast house (roof area 175m) using a 5KL system for hot water, laundry, toilet flushing and external uses.

The cost to install a 5KL rainwater system in an existing house is less than $3,000 when all houses are supplied. This is less than the cost of installing rainwater supply into new houses, for which installation is mandatory.

Wyong Council and the National Water Commission dismiss rainwater tanks as an option for future water supply without comment on the costs and yields involved. But subsidies for rainwater tanks would not be necessary when the cost of installation is $3,000 with yield of 93KL.

Ian Mott talks about asynergy, “a condition where the collective intellect of a group is substantially dumber than the sum of the individual minds that make up that group ... not necessarily a synonym for government policy and administration, but many have observed a very strong association between the two.”

Why are rainwater tanks dismissed as an option for the Central Coast?

Greg Cameron

In answer to your last question, Greg. They refuse, at all costs, to grant any credence to a solution that does not include the perpetuation of their role. They have placed their own continuity above the interests of the community they serve.

Perseus/Greg,
Just a friendly question, are you both accountants or statisticians, the reason I ask is that you are so precise with figures, yet have no idea how ordinary people actually live.

Tubley,
Long time no hear, may need your help in near future, if you could contact me on my regular address please comrade.

Does anyone know if any of those who are required to install tanks are able to enjoy reduced water fees by accessing less mains water . Or do fixed water charges still generally apply ?

Here in tas some councils charge a flat rate per household & some charge partially by volume taken .

If in those places where rainwater tanks are mandated fixed charges still apply the point made by perseus is proven .

Yes, Jammo, in Brisbane you still pay over $110 a year for the access charge even if you use no water from the mains. I have deliberately left this out of the water costings because it is effectively a tax, not a water charge. But when you include this in the water costings it increases the average cost/KL by 44 cents at average use and much more if you use less anyway.

With a 13.5KL tank and an average use from the mains of only 35Kl it lifts the cost of this residual mains water by a massive $3.14/KL.

The irony is that they justify this water charge on the need for fire fighting supplies but this is also complete bull$hit. Every second house in Brisbane has a swimming pool with more than 30KL in it and a minor change in the emergency laws could enable this to be used on those rare occassions when a fire occurs in your street. There has been none in mine for at least 16 years.

Centralised high volume water was best practice in 1900 but these days, with improved tank and pipe technology, mains water can be delivered to a tank by small low cost trickle systems that fill it up over night rather than full pressure on demand.

And Shonga old boy, pull your head in, 3 of my 4 houses have water tanks so I am both an accountant, and a person who knows what happens on the ground.

Perseus,
Just for the record "old boy" I don't take orders from the likes of you or anyone else for that matter, you may get away with intimidating others on a daily basis, but that won't happen with me.

As you have answered my question adequately I have no further questions, you obviously wouldn't have a clue how the averege person lives because the average person does not own 4 houses. And you admit to being an accountant which speaks volumes.

You have my sympathy, if one day you crawl out of you cocoon and realise how the average family survives on little pay, you may then realise how poor your own money management skills are, until then, I wish you all the best, as life comes and goes, whether or not you own 4 houses, the object of the exercise is to enjoy life, not duplicate old Scrooge.

Re the percentage of houses, Greg. There is no reason why water tanks cannot be used by Semi-detached houses and townhouses. These have correspondingly smaller gardens and usually have fewer people in them. The smaller the roof area the smaller the garden or the more likely it will be paved not lawn. This will drop daily use from 700L to 500L a day so the size of the tank can drop in proportion.

A reduction in members in each semi-detached household will also allow a smaller tank to meet the same proportionate requirement.

This will lift the percentage of households that can use tanks from 76% to 85% before we start to look closely at capturing water from shopping centre roof to supply apartments.

Get real Shonga, you took a poke at me, I asked you to pull your head in, you then have winge about not being intimidated. Give us a break.

Perseus,
Apologies "old boy" I had no idea you had such a delicate, sensitive nature, the thing is that I support your arguement to a large extent, however you must realise the limitations of ordinary people financially to comply with these great ideas.

Cost is the chief argument used by politicians and their advisers to reject rainwater tanks as a source of water supply for every household in Australia.

Governments pay subsidies for rainwater tanks because costs are too high. But if all households have rainwater tanks the cost will be affordable making subsidies unnecessary.

Shonga asks how can ordinary working people afford a rainwater system? The system that I propose costs under $3,000 comprising 5KL of capacity yielding 75KL/year or 2.25ML over 30 years. (Perseus and Ian Mott will spend more to have 13,500 litre rainwater systems installed, as is their right and good on them.)

The low cost is guaranteed when all houses have a rainwater supply installed. One way to achieve this is for all State Governments to mandate reduced mains drinking water consumption at point of sale of all property, with rainwater tanks deemed to comply.

Dwellings are sold on average every seven years. In a decade, most houses in Australia will have changed ownership. There are 7.1 million dwellings in Australia of which 5.3 million are separate houses. With 700,000 installations a year for 10 years, watch the prices tumble as suppliers compete and innovate.

At under $3,000, a 5KL rainwater supply is less than 1% of the cost of a house – new or existing. Lowest cost financing is when the rainwater system is financed as part of the property transaction. People who rent are protected because the owner of the property purchases the system.

At the heart of the policy issues lies the question of ownership of rainwater. State Governments actually refuse to confirm or deny that water collected from roofs for rainwater tanks is owned by the building owner.

If Governments simply acknowledged that the owner is the building owner, it is a simple next step for all State Governments to mandate reduce mains drinking water consumption (water that is owned by the State) with rainwater tanks deemed to comply.

Governments will not even examine this proposition. They do not acknowledge the facts and data when presented to them. Can anyone suggest why?

Greg Cameron

Greg,
While appreciating your good will and intellegent suggestions, $3,000 may as well be $1 million to most working families, it is akin to offering a Rolls-Royce to a working family at half price, while it reresents a terrific bargin, the family is still unable to afford the wheel covers.

Highly paid people [ no insult intended ] seem to believe that everyone in the community recieves the same remuneration as themselves, nothing could be further from the truth. The first person who can show me a shop assistant on $56,000 per annum, will have a commitment from me, that I'll bare my bum in Bourke Street, if such a shop assistant is found.

Even though I am debt free I could not come up with $3,000 unless I prostituted myself, which is something I wouldn't do. All I am suggesting is now that both you and Perseus have identified the problem and the solution, please devise a way to get the plan off the drawing board and under construction. The sticking point is that $3,000 is about $2,700 more than an ordinary working family can afford.
Regards, Shaun.

Shaun – as a person who is debt free, you are one of the 40% of householders who owns the dwelling they occupy. Of the other 60% of dwellings, about half are occupied by people who have a housing loan and the other half are occupied by people who rent.

You’re dead right: $3,000 cash is too much for an ordinary person to stump for their private drinking water supply using rainwater tanks. This is why I propose that you find the cash when you sell your house, which, if you live in Sydney, is now worth about half a million, give or take. If you want to install a rainwater supply system earlier, you are able to borrow the money at competitive rates against the value of your property.

Dwellings are sold on average every seven years and this, obviously, generates the cash to purchase a rainwater supply system. My proposal to make reduction in mains drinking water consumption mandatory at point of sale, with rainwater tanks deemed to comply, assumes that rainwater is owned by the building owner.

Ownership is relevant because the person who owns the water is legally responsible for its quality. The Government will not accept responsibility for rainwater being drinking quality. Non-drinking quality water may not be connected to your household plumbing system – separate plumbing must be installed. If Government owns the water you collect in your rainwater tank you will be required to install costly separate plumbing.

You should be more concerned about Government regulating the water that you collect from your roof and setting an entitlement for you to use this water.

According to the National Water Commission, no entitlement to use the water collected from roofs for rainwater tanks is specifically issued under a water management Act. “Entitlement to (not ownership of) the water captured would by default rest with the building owner, provided that it has been captured in accordance with whatever regulation might apply for rainwater tanks in each jurisdiction”. In other words, Government wants to be able to tax you for using rainwater.

Greg Cameron

Greg,
I appreciate your logic and common sense approach, I am debt free, however I wish to stay that way. On a low income, meeting any repayments put one in grave danger of losing everything. What I am saying is were I to borrow $3,000 and repay it of course with interest, and a week later my car breaks down needing major repairs, which I must undertake in order to continue to work, I then find myself unable to meet repayments, and in the worse case, which always has to be a consideration on low incomes, I have my home sold out from underneath me so the Bank can retrieve it's $3,000. Would this be a fair assesment?

Shaun,

The safety net in my proposal is that you do not buy a rainwater supply system unless you buy a new house, or undertake a major renovation of your existing house, at which time the law requires you to reduce mains drinking water consumption with rainwater tanks deemed to comply.

Greg

Greg, the reason the governments will not confirm that the rain on your roof is your water is that they are busy trying to claim that the water that falls on a farm belongs to the government. This is in direct contradiction of all the legal descriptions of freehold title which include "waters" etc.

The very same people who were once trying to nationalise all means of production (until it was proven to be a complete failure) are now trying to nationalise ecological values.

The interesting legal point is that if the rain is owned by the state then surely it must be the responsibility of the state to fix my leaky roof and to fully compensate me for flood damage etc.

The key to resolving this issue is to view the roof as an "improvement", the benefits of which accrue to the improver. But once that was recognised the homeowner would become responsible for the cost of disposing storm runoff. Not a problem if one has a good tank.

But that also raises an interesting question of the cost of storm water disposal that will be saved by a tank. This should be included as part of the economics of the tank and certainly justifies a large part of the government tank rebate.

Thanks Greg,
Perseus, despite a bit of to and fro I am very interested in this debate, and hope to progress my knowledge, as Greg has done with me, I also value your contribution, the thing is if the concepts could be harnessed in a way that makes it affordable for not only new home owners but those like myself wishing to make a contribution to the saving of water, but are bereft of finances to do so, how can we help.

Also I would be interested to know both your opinions on Tully, the wettest town in Australia, N.Q. RE an engineering capacity to harness some of that rainfall for use by the balance of the country.

Also is there any way that agriculture could become more efficent with water use, as they are collectively the largest users of water, is anything being done in this regard?

Perseus, "But that also raises an interesting question of the cost of storm water disposal that will be saved by a tank. This should be included as part of the economics of the tank and certainly justifies a large part of the government tank rebate."

Does use of tanks actually lessen the need for storm water disposal capacity?

I suspect that councils would still need to maintain storm water disposal systems which could handle storm runoff once every bodies tanks were full.

I'd heard in the past that one of the reasons tanks were opposed is that storm water runoff was important for maintaing the storm water drainage. High volume flows are needed to flush the pipes. It's quite likely that the same kind of flushing is required in the waterways which storm water systems empty into.

If the above assumptions are true tanks may actually add to the cost by increasing the maintenance required on storm water systems.

Any thoughts on that aspect of the use of tanks?

R0bert

One practical way you can help to achieve the lowest cost of rainwater supply - and supportive Government policy if you want a rainwater supply before selling your existing house - is to ask your local member of parliament whether you own the water you collect from your roof for your rainwater tank; and whether the Government intends to restrict your right to collect and use this water.

No State Government will confirm that water collected from roofs for rainwater tanks is owned by the building owner (Western Australia and Queensland Governments confirm that the water is not owned by the State).

The lowest cost per kilolitre of rainwater is achieved when rainwater tanks are plumbed for at least hot water, laundry and toilet flushing uses and the plumbing is shared with mains drinking water supply.

It is a matter of personal choice if rainwater is also used for actual human consumption.

If water in rainwater tanks is owned by the Government, the uses will be restricted to toilet flushing and outdoors and separate plumbing will be mandatory.

This is because the quality of rainwater is the owner’s responsibility and where the owner is the building owner they have the legal right to use rainwater for any purpose upon their own responsibility.

The current cost of rainwater tanks and their installation including plumbing is a function of demand and current demand is insufficient to warrant investment in large scale manufacturing facilities and installation services to generate lowest costs.

A solution is mandatory reduction in mains drinking water consumption at point of sale of all property in Australia, with voluntary collection of water from roofs for rainwater tanks being deemed to comply. Ownership is the deciding factor.

If this solution is implemented by State Governments, investment in large scale manufacturing facilities and installation services will be warranted because dwellings in Australia are sold on average every seven years which will underpin demand. Payment of Government subsidies will not be necessary because the cost savings generated by economies of scale are worth more than the subsidies.

Greg Cameron

In response to RObert, let’s establish how much water is involved.

At least 800 billion litres (800GL) of water was discharged from roofs of all buildings in Australia in the 12 months to 30 June 2006. Of this amount, an estimated 670GL was from roofs of separate houses.

The ABS predicts Australia’s population will increase by 5 million and reach 25 million people in 2032. This represents a 25% increase in the population of Australia.

530GL of rainwater collected from roofs for rainwater tanks is sufficient to meet the drinking water needs of 5 million Australians at per capita consumption of 290 litres per day.

As discussed above, ownership of rainwater is the primary determinant of the potential for rainwater to provide 20% of Australia’s drinking water requirements by 2032.

Rainwater tanks convert urban stormwater generated from roofs from being a cost to being an asset.

Urban stormwater systems routinely fail when subject to the first rush of water from a rain event - they leak under pressure. This is because roofs collect rainfall and discharge this water at a single point (the stormwater drain) however this water also has considerable velocity and pressure because it is flowing with the force of gravity (off the roof). The pressure causes stormwater drains to leak and if the storm is big enough, the drainage capacity is exceeded and flash flooding occurs.

An empty 5KL rainwater tank will contain the first 28mm of rainfall from an average roof area of 175m. This leaves the stormwater system free to carry the first rush of water discharged from non-roof sources.

Leaking stormwater drains erode roads from beneath, creating potholes, another cost. In the natural environment, 90% of rainfall stays where it occurs. In the man-made environment 90% of rainfall leaves the point where it occurs. Urban designers are now trying to reduce the need for stormwater drains by water sensitive urban design – which means trying to keep rainfall as much as possible where it occurs so that natural systems can take over.

Greg Cameron

Shonga, the easiest way to save water is to divert the water from your downpipes onto your garden. I use the base of a palm frond because of it's curves to divert the flow from the bottom of the pipe before it goes down the grate. This will ensure the lawn gets a good soaking from even a small fall and can easily be removed if a wet season looks like delivering too much water.

The other point to make about the economics is that the cost of a tank is merely a pre-payment of the money you already pay for mains water so on a cash flow basis it is the only sort of household debt that you know you already have the money to cover.

Re the Tully Millstream, it would seem that the easiest way to protect the Great Barrier Reef from excess fresh water (that kills coral faster than silt) and siltation is to build a decent dam so most of the silt remains up stream. The remaining flood flows can then do their bit for fish and prawn life cycles. But don't say that to an ideological green "Bimbecologist" who simply cannot countenance a dam having any beneficial effects.

Robert, most of the problems of urban storm flooding stem from the greater catchment efficiency of roofs and pavement. So if even 50% of houses had tanks the remaining roof and pavement area will still deliver a significant surplus of storm water compared to natural runoff from forest or pasture. And there is always at least one wet season rainfall event that will make the tanks overflow and give the system an annual flush.

Good points, both. And I agree with Greg, write to the Minister for DNRM to ask him who owns your roof runoff.

Perseus/Greg
Thank you both for your invaluable advice, much appreciated.