Sylvia,

For the detailed analysis of my costings go to this item published on 18 July (third from the bottom)

http://forum.onlineopinion.com.au/thread.asp?article=6112

For the source article, “Water rights - your roof, your tank, your water, right?” go to

http://www.onlineopinion.com.au/view.asp?article=6112

As always, your forensic financial analysis will be appreciated.

The central proposition is that rainwater supply sourced from the roof is a cost of housing, the same way that a stove and hot water service are costs of housing – they are not “optional extras”.

In relation to your comment about the network utility operator’s cost of delivering water, I have asked all State Governments and the National Water Commission to evaluate my costings. So far, none have managed to do so. The water utilities can, if they wish, integrate rainwater tanks into their water management systems. Using wireless communication, the performance of rainwater tanks, including holding capacity at given point in time, can be centrally measured. Rainwater tanks can be fully integrated into a network utility’s operations. One of the many benefits is water trading – the utility can sell a household’s saved mains water on the open market and share profits with the householder. The fact that network utilities are not prepared to assess rainwater tanks on their technical merit is of concern. My view is that rainwater tanks will lower water costs for households, increase profits for network utility operators as they cater for an expanding population, and benefit the environment. It is for this reason that it is important to establish who owns the water that falls on a person’s roof. Answer me this: do you own the water that falls on your own roof?

Greg Cameron

Lyn Allison fails to inform as to what entity will construct and operate the proposed desalination facility, and how its product will be 'sold', let alone provide any projected cost figures for desalinated water.

She also fails to state what method of desalination will be used: is it Reverse Osmosis (RO), or is it multi-effect distillation?

She fails to state specifically from where power will be supplied, although quoting a broad-brush figure of increasing Victoria's greenhouse gas emissions by 2%, and asserting that desalination is an "highly energy intensive process".

She makes the somewhat unclear statement that "And yet the amount of water processed will only produce the equivalent of that required to power two of the regions four coal-fired power stations." What does this really mean? Did she mean to say ".... the amount of water processed will require the power output of two of the region's four coal-fired power stations."? If she did, it is surprising that coal-fired electricity generation apparently contributes so little to total greenhouse emissions, percentage-wise. All very unclear.

All just 'desalination is bad'!

Lyn, and many others in public life, would do well to research some of the OLO discussions that have touched upon desalination as a component of the overall water supply situation for Australia's urban centres. They would do particularly well to examine some of the discussion upon Peter Ravenscroft's article "What's a bone-dry city worth?" See: http://www.onlineopinion.com.au/view.asp?article=5616 for the article, and http://forum.onlineopinion.com.au/thread.asp?article=5616 for the thread.

There seems almost to be a resentment of the prospective independence of desalinated water supply from the vagaries of rainfall in a country where such fluctuations have long been par for the course.

With the expanded, and still expanding, urban populations of Australia, the "more sustainable and cheaper alternatives" of which Lyn speaks in actuality have long belonged to others outside the urban centres. They are not Melbourne's to develop or take.

Time urban Australia paid its dues.

Greg,

See the spreadsheet at

http://www.cryogenic.net/rainfalltank.xls

Assumptions:

A house with a 250 square metre roof
Three people with average 230 litre per day consumption
One third of consumption sourced from rainwater tank when available.
Real interest rate of 4%
Actual rainfall in Terrey Hills from September 2006 to August 2007.

Water pump costs $581, and lasts 12 years, and then has to be replaced.
Tank lasts 25 years.

Pricings from http://www.irrigationwarehouse.com.au/

I based this on yearly payments. It would work out a bit cheaper on monthly payments, but not much.

The lowest cost of water I could get was $1.98, based on a 5000 litre round tank (i.e., the cheapest kind). A 2000 litre tank gave about the same result. Either smaller than 2000 or larger than 5000 pushed the price up.

The overall reduction in reticulated water consumption for he 5000 litre tank is 31%.

If we assume four people in the house, with a 5000 litre tank, with the same per capita water consumption, then the price drops to $1.65 per litre, though of course this is assuming that the pump still lasts as long despite the increased usage.

The results are clearly sensitive to assumptions, but I think one would struggle to get the cost down to something acceptable without assumptions that look highly implausible.

As regards the water utility using remote sensing to measure tank capacities, I don't think that undermines my argument about the delivery costs. I would expect tanks over the entire metropolitan area to empty at similar times, because they're largely exposed to highly correlated rainfalls.

I don't understand the point about water utilities selling on the open market water that has been substituted by rainwater tank water. The premise for installing rainwater tanks is that there is not otherwise enough water.

Sylvia,

One method for collecting water from all downpipes of a house is to have a rainwater tank installed at each downpipe. The tank used in my cost estimate is a 670 litre tank, so selected because it can be conveniently installed in all but the tightest spaces. A 670 litre tank will cost $150. A pressure pump will cost $150 and our conservative estimate is the use of four pumps over 30 years. Automatic switching valve cost is $200. System installation and plumbing estimated cost is $1200, based on four inter-connected rainwater tanks collecting from 175 square metres of roof area. These costs can be delivered with modest economies of scale, around 5000 households. The cost estimates are easily validated.

Based on 85% mean annual rainfall (which means that Sydney’s desalination plant will be required just to make-up the shortfall for existing consumption, let alone a 25% increase in population) the cost of rainwater for one million households in Sydney (separate houses) is $1.25 a kilolitre for around 80KL each year. This makes rainwater the lowest cost source of additional water supply. The assumption is that rainwater is used for at least hot water, toilet flushing and laundry.

When Sydney Water starts charging $1.60 - $2 for mains water, to pay for the desalination plant, the premise for installing rainwater tanks will be to secure a lower cost of water. When everyone runs out of rainwater, they revert to mains water, and will consume all of the desalinated water that this plant is able to produce. When one million households use 80 KL of rainwater this is 80 GL of water that remains in storage. When this volume is sold for $1.60 - $2 a kilolitre, obviously, profits will be made. The alternative – not to build the desalination plant – has been ruled out by the Government on the basis of risk.

Greg Cameron

This article makes sweeping statements and generalisations, with no evidence. An appeal to emotion that is sadly typical of what passes for political debate these days.

Where are the true environmentalists? For decades we've been diverting water from our natural rivers and lakes, and now even from our farms. A properly designed desalination plant has negligable impact on its local environment and can be powered from non-carbon emmitting sources.

Let's MAKE the water we want to use, like any other commodity. I for one don't mind paying a little more for this necessity. I want to see our rivers flowing freely again.

Also, don't forget that domestic rainwater is not "unused" at the moment. It flows into our storm drains and then into our bays or rivers, flushing them out. Capturing a significant fraction of this and diverting it to the sewers, may lead to poor outcomes.

GC, with your system, if you get more than 15 mm of rain, your little tanks will overflow.

K Katulla
"Where are the true environmentalists? For decades we've been diverting water from our natural rivers and lakes, and now even from our farms. A properly designed desalination plant has negligable impact on its local environment and can be powered from non-carbon emmitting sources."

I suggest you give us an example of the power sources you envisage for the rather large amount of power required.

David