Can someone explain the reasoning here?

I'm not sure I understand; growing food is a waste of water? Granted, there is some waste when irrigating, and there are some ways of conserving with small gardens, such as drip irrigation, but how is a larger farm, or one in a poor country that cannot afford fancy plumbing, expected to water crops? I'd like to get some of those engineers and theoreticians out on a farm or ranch for a few weeks...