Craig Wilson is California's first Delta watermaster, a position created by sweeping water reforms lawmakers passed at the end of 2009.
In his first report to regulators, Wilson will argue Wednesday that farmers who use water inefficiently are violating the constitution's requirement that its use be "reasonable."
His recommendations, if adopted, would mark the first time the doctrine has been applied so broadly.
"It's been taboo," said , a noted water expert and president of the , an environmental research organization based in Oakland. "No one has wanted to step up and say, 'This is not a reasonable or beneficial use of water.' "
Gleick added: "We don't have enough water anymore to be able to avoid that conversation."
Wilson, a lawyer, contends that more efficient water delivery systems and irrigation practices already are in use in some farm regions, particularly where water is more expensive, and that they should be required elsewhere.
"Persons who do not employ some or all of these technologies, where they are economically justifiable, locally cost-effective and not harmful to downstream agriculture and other environmental needs, are simply using water unreasonably," Wilson wrote in a report to the State Water Resources Control Board and the new Delta Stewardship Council.
His recommendations include setting employees to policing wasteful practices and requiring water agencies that serve farmers to develop more sophisticated water-delivery systems.
Farmers in California collectively use about four times as much water as the state's cities, suburbs and industries, and that is why Wilson focused his first report on water use on farms.
A 2008 report by Gleick's organization found that California's farms could reduce water consumption 10 to 15 percent by adopting techniques some farms use.
Wilson said he does not expect his recommendations to yield that much in savings, but even a statewide improvement of 1 or 2 percent would yield hundreds of thousands of acre-feet of water enough, potentially, for millions of new residents.
"I'm basically saying there's some significant savings, but it's not the same others are talking about," Wilson said.
Part of the reason that Wilson sees less potential for savings than others is because not every of water that is left unused is truly saved, he said.
That is because much of the water diverted from rivers and wells to farms is returned after it drains back into rivers or seeps into groundwater basins.
It is only the water that would have been taken up by crops and weeds, evaporated, or otherwise consumed that can be counted as conserved, Wilson said.
Water in Western states such as California is neither infinite nor unnecessary, which is why the right to use it has always been conditional. The constitution requires anyone using water to put it to "beneficial use," and that use must be "reasonable."
What is reasonable has never been fully defined, but environmentalists and, increasingly, some state water officials, are pointing to those concepts as ways to promote better water policies.
Many, and perhaps most, of the state's farmers use water efficiently, Wilson said.
Still, some agricultural organizations are likely to oppose new regulations.
"There are a number of recommendations in there that are concerning to say the least," said Mike Wade, executive director of the California Farm Water Coalition.
Wade said the recommendations go too far in equating water-use efficiency with reasonableness.
"The micromanagement that is being proposed in this report is unprecedented," he said. "The industry is enormously efficient."
Wilson will present his report Wednesday to the State Water Resources Control Board, which is not scheduled to take any action. He will later present the same report to the Delta Stewardship Council.
Mike Taugher covers the environment. Contact him at .