There are only really two things that we cannot live without: food and water.
Each of us drinks about four litres of water every day, through various kinds of liquids. But it's the food we eat that is really water intensive. It takes about 2000 litres of water to grow the protein, cereal and vegetables that we eat every day.
That means the average Australian needs over 700,000 litres (around 20 average-sized backyard pools) just to grow the food they need to survive.
This brings me to the Murray-Darling Basin Plan. I find it strange that the discussion of this plan focuses only on its environmental impacts - its affect at the mouth of the Murray, the 16 Ramsar wetlands and over 2000 other environmental sites within the basin.
But we rarely discuss the food the basin produces, even though it produces 40 per cent of our food, including 90 per cent of our tomatoes and almost 70 per cent of our oranges.
We have always to look at the other side of this equation. When we are talking about water and the environment we are also talking about our capacity to feed people.
In a sentence, the basin plan will take water from food production and use it to ''water'' the environment. That means we will grow less food.
The plan proposes to take around 3500 billion litres away from food production (this includes water returned before 2009). That means that if each Australian needs 700,000 litres of water each year to grow the food they eat, one of the costs of this plan is that we won't be able to feed 5 million Australians that we could before.
That food will have to be produced elsewhere in Australia or imported. There are issues with both of these options.
The party for the man in the koala suit has effectively placed a veto on the building of dams in the future. Water is wealth and if you can't supply reliable water you can't create agricultural wealth.
Dams are absolutely essential to providing water reliability and supporting irrigation. About half the agricultural profit produced in Australia comes from the 2 per cent of agricultural land that is irrigated.
It is a myth that Australia does not have the potential to produce more dams. We use just 6 per cent of our available water, less than the world average, and less than in Asia, Europe and America.
We still have potential, particularly in our north to expand irrigation and food production but until governments can stand up to green lobby groups this option may be a fair way in the future.
The other option is to import our food. I don't think that is something most Australians want. It is hard enough to buy an Australian fish, and we don't want to make the entire fresh-food section into the grocery equivalent of a Contiki tour.
But even putting that aside, the environmental equation is just as much of a dilemma overseas as it is here, if not even more fraught.
The main aquifer used in North China that feeds 130 million people has dropped three metres in 10 years. Some farmers are pumping from 1000 metres below the ground for their water. The World Bank says that unless water use is brought into balance, future generations face ''catastrophic consequences''.
India has drilled 21 million irrigation wells. In North Gujarat, the water table is falling six metres a year. The impact of the coal seam gas industry is very concerning for many Australian farmers. Yet a recent report showed that aquifers would fall at most by about two metres. Still a concern, but, nothing like in North Gujarat.
The cradle of human civilisation, the Middle East, is perhaps the most exposed. Syria's grain harvest has fallen by a third since 2001 and Yemen's has fallen by half over the past 40 years. Saudi Arabia's aquifers are largely depleted and it is phasing out wheat production. There simply are not vast untapped plains overseas for the human race to exploit. We have the choice between using water for food or for the environment. But let's not kid ourselves, if we don't grow food we make life tougher for other countries that can't do it for themselves.
It's an iron law of the national accounts, that your imports must equal exports (after including flows of capital and income). We may think we can be environmental angels here, but when we replace domestic production with imports, we simply export an environmental problem overseas.
Barnaby Joyce is the Nationals' Senate Leader and the opposition spokesman for regional development, local government and water.