Because the invisible hand of the market will provide as much as we want.

The private sector can replicate the outstanding job it has done at meeting the global demand for food and thereby ending world hunger <sarcasm>.

The US exported 136 Billion dollars of agricultural goods last year. I wonder how many people that fed.

From wiki: http://en.wikipedia.org/wiki/Seawater_desalination_in_Australia

Seawater desalination in Australia is the desalination of, or removal of salt from, seawater in Australia.

Background

Until a few decades ago, Australia met its demands for water supply, drawing freshwater from dams and water catchments. However, during 2000-2010 a significant lack of rainfall drained water reservoirs.[1] The most affected cities have been the capitals, where there is high water demand. In 2007, Sydney, the capital city of New South Wales, experienced a dramatic drop of its main dam Warragamba, where water levels dropped to 33% of normal.

Australia’s first desalination plant was constructed in 1903 to treat saline groundwater in the gold fields of Western Australia at Kalgoorlie.[2] A lot of desalination plants were built in Australia between 1960 and 1980 where there was a world membrane technology revolution. Most of them were reverse osmosis plants, as well as vapor-compression desalination and multi-stage flash distillation plants. By 2002, however, only two reverse osmosis desalination plants were still operating, the first in Kangaroo Island and the second in Rottnest Island.[1] Seawater reverse osmosis is the only type of desalination technology currently used for large-scale desalination plants in Australia, the most important of these plants are located in Perth and Sydney.[2]
[edit] Desalination

Compared to existing sources, desalination is considered to be expensive, but research is underway to develop more effective desalination technology.[3] Despite its drawbacks, it is considered a possible solution to the country's water shortages.

Australia is the driest inhabitable continent on earth and its installed desalination capacity is around of the total world’s desalination capacity. The Department of Agriculture, Fisheries and Forestry has considered several desalination technologies processes in Australia [1]:

Reverse osmosis
Electrodialysis
Multi-stage flash distillation
Multiple-effect distillation
Vapor-compression desalination
Solar humidification
Membrane Distillation

In Australia many desalination plants are utilizing wind farms to produce enough energy to operate nearby desalination plants. For example, the Kurnell Desalination Plant, with a capacity of producing 250 million liters (ML) of drinking water per day, supplies 15% of Sydney’s water needs via RO technology and is powered using “100 percent renewable energy” from the 140 MW Capital Wind Farm.[10][11]

The availability of renewable resources as well as their fluctuation in electricity production from region to region requires a customized design for each desalination facility. In order to maintain steady-state operations many facilities utilize renewably produced energy while connected to a smart grid, importing or exporting energy to the plant as required. The Perth Seawater Desalination Plant utilizes this strategy where 48 wind turbines produce 80MW on the Emu Downs Wind Farm to provide an overall 24MW to the desalination plant.[12] Electrical energy from the renewable energy can also be stored in storage batteries and utilized when needed. As seen in the PV-powered RO system in Gillen Bore, Australia; producing 1,200 L/d.[13] Or if the plant is not required full-time, it can operate using the power as it becomes available. In 2005 a PV-powered hybrid UF/RO filtration system providing 764 liters per day tolerated well power variation from changing weather conditions.[14]

However, there are limitations in the ability of renewable sources to provide for desalination facilities. Desalination is a continuous process while renewable energies provide inconsistent power. For any new desalination installation to claim it will be powered by renewable energy, additional renewable energy should be generated.

...more at the link.

Then proceeded to sell off half the parts.

When water gets pricey enough, desal may work, but before that point things will get ugly.