Some very simple arithmetic that very few people seem to bother about:
My family can live quite comfortably on 3000 litres/week. That's 156000 litres a year. If one mill of rain on a square meter of roof = 1 litre, and if the average rainfall in my area is 1000mil a year, how much roof do I need to be sustainable?
I get 156 sq. metres, or a roof 12.5m sq. Not a very large house. As rehctub points out, all that water can be reused. (we redirect washing machine water to the veges, waste water onto a paddock).
Instead of building dams, we would be better off if our governments spent the money on water tanks.
For agricultural purposes, untreated water is far more effective than treated water.

Grim I have always wondered why the old backyard water tank went out of favour. We installed a 5,000 litre tank in our garden a few years ago to water the vegies and fruit trees and I don't know why we can't all do the same.

Domestic water use is low compared to agriculture. Your idea of using grey water for agriculture is sound and it can be treated by running through reed beds prior to being used for food crops. I know of some councils who have done that for rural estates (as much as I hate contrived rural estates).

A question (or two) for Grim and Pelican.

Why would the government favour individuals saving on water, energy and other resources when it can subsidise business to build water desalination plants and other private (for profit) enterprises and receive hefty 'donations'?

Why "clean" coal?

Why invest in nuclear?

While these are rhetorical in nature, they are also serious questions. And I am not very happy about the answers.

These articles by Colin Chartes are great. Always clear with easy to understand logic. After reading them though I always think they are too staid and academic. “Oh by the way we won’t have enough water to grow all the food we need in a few years. Nice to see you. Give my love to the wife and kids. See ya.”

He says it is a crisis but there is no Crisis-worthy passion. Maybe that is the best way to get a reasoned response.

He also says the 2.5 billion increase in the worlds population will have to exist on 2500 calories a day. That is not much food. Is that the world we are aiming for? “Hey all you new 2.5 billion, you’ll be living in poverty.”

I’m glad he mentioned Pakistan. Much of the food Pakistan grows is irrigated by the Indus River. Pakistani farmers take about 80% of the water out of the Indus River to irrigate. The population is likely to increase by 85% (150 million) in 40 years. They are already running down aquifers. Where will the water come from to grow the food to feed the 150 million? It must come from outside Pakistan.

The Pakistani government doesn’t even control much of the land shown on the map. Half the population is illiterate. Pakistan is the 170th richest country in the world with 24% of the population living under the poverty line. Is this the kind of country that is going to be able to implement complicated water pricing systems and new water saving irrigation methods?

These aren’t their only problems. The majority of the water that flows in the Indus, doesn’t originate in Pakistan. About 60% of the catchment is in dry (<300mm / year) Pakistan, but most of the water flowing in the Indus comes from Chinese controlled Tibet and Indian controlled Kashmir. China just built a dam on the Indus in Tibet and didn’t tell the Pakistanis. India and Pakistan’s conflict in Kashmir is longstanding. Now let's throw in Nuclear weapons and terrorist hideouts.

That is a crisis.

150 million in Pakistan? An example of many countries with huge populations where soon if not already, the land and water will be insufficient to properly feed them all.

It will be sorted out on an evolutionary scale. As with animals, if they breed excessively, there will be a high mortality as the strongest in their part of the globe grab the most resources, so it will balance out.

If we keep dishing out a stack of aid to 3rd world countries who do not have in place population control programs, and a full range of reproductive health services that women can confidently access, without issues with cost or persecution, it is irresponsible to keep giving out aid without these issues being addressed, because they will not change their behaviours and keep up contributing to their own hardships.

ie perhaps its better to reduce aid to such countries by 10% annually until it either reaches nil, or they take steps with population control and reproductive health, then higher aid can be restored as needed.

rehctub: "I am of the opinion there is enough water, it's just that we take it for granted."

You seen to be talking about the water situation in Oz; the article was discussing the global water situation. That aside, we in Oz do appear to have hit a limit. Whereas before there was no pain when we added a person, now it means we must all reduce our water usage accordingly. As you say, this is possible. But which do you think is better - keep making sacrifices to reduce out water usage, or lower immigration so we don't have more mouths to water.

You also seem to think most of out water consumption is for household use. It isn't. It is used in food production. Thus using tank water at home doesn't solve the problem - it just helps in a small way. We accommodate new people by exporting less food, and one hopes by importing correspondingly less and lowering our standard of living accordingly.

Movingpast: "Addressing the forum comments first- 'overpopulation' is not the problem"

Movingpast: "Chartes' solutions only delay the problem"

What an odd pair of statements to appear in the same post.

When an entire country has run out of water population most certainly is the problem. The countries population has grown beyond of its land to support it. Sure, the country can import food - if they can afford it, but if the population keeps growing that only delays the inevitable. The inevitable is famine, and the population reduces for a while. This is just stating the obvious; repeating what is historical fact. It has already happened several times in my lifetime, and probably yours.