It's amazingly easy to steal water from a California stream. Even in this epic drought, the state has no way of monitoring exactly who is tapping into its freshwater supplies and how much they take.
And those who do get caught taking water they have no right to often are allowed to keep taking it for years just by promising to obtain a permit.
Nearly 30,000 entities in the state hold valid water diversion permits, including individual property owners, farmers and water utilities.
Some have meters or gauges to measure their diversions, but the state has no ability of its own to monitor those gauges in real-time.
People and entities with water rights are required to regularly report their water use to the state, but many don't, and the state has no way of knowing whether their accounts —self-reported — are truthful.
In average water years, many of these issues don't matter much. But the weaknesses are expected to complicate matters this year as the state struggles to stretch limited water supplies during the worst drought in 40 years.
This spring, it is likely the State Water Resources Control Board will order some water rights holders to divert less water to ensure enough flow for cities and wildlife, something that has not been done since the drought of 1976-77.
The state's ability to enforce such curtailment orders will be sorely tested.
Water board officials acknowledge the weaknesses, and say they will do their best within existing legal constraints to police the system.
"We know for sure, unless we get another 40 days and nights of rain, that there are going to have to be curtailments," said Andy Sawyer, assistant chief counsel at the water board, the state agency charged with regulating California's complicated system of water rights.
"The basic idea is to live within our available water supply ... so we don't have people stealing from each other.
"And frankly, under existing conditions, for a lot of people it's just cheaper to violate and pay the penalty than it is to comply."
A basic principle of California water is that all the fresh water in the state's lakes and streams belongs to the public at large. It's possible to get a state permit to use that water for a domestic or commercial purpose.
But the permit usually comes with limits on the amount of water that may be diverted.
Water permits or rights are held by all kinds of Californians: the rural homeowner who wants to fill a pond from an adjacent creek; the city that needs to tap a river to serve a growing population; the farmer who diverts water to grow wine grapes.
But they generally fall into two classes.
Any permit issued after 1914 is considered a "junior"water right and comes with stricter limits on how much water may be diverted and when. Violate those terms, and you're stealing from somebody else: a city or farm downstream, or the fish and other creatures that need water to survive. These are the first class of water permits to face curtailments in a drought.
The "senior"class of water rights are known as "riparian" and "pre-1914." They generally include more supply and fewer diversion limits, if any. The state has no legal authority to impose fees on these diverters, and its ability to inspect their diversions is limited.
But even these senior diverters are banned from "waste or unreasonable use"of water, and they could face curtailments this year due to the severity of the drought.
Having a water right means you don't have to buy water from somebody else. Instead, the water is free and you control access.
Junior water rights usually include a nominal annual fee paid to the state, but otherwise the same easy access applies.
This differs from homeowners or water contractors who pay a monthly fee that varies according to how much water they consume — and who, if they don't pay, see their water cut off.
In a drought year like this one, water rights get stretched even thinner, and the temptation to cheat grows.
Water theft can take many forms. An illegal marijuana grower might lay pipe in a mountain stream to irrigate his illicit crop. A farmer with a valid water permit might take more than his permit allows to expand his crop or protect it from drought. A homeowner may decide to build a pond for swimming and divert the closest creek to fill it without getting a permit from the state.
The State Water Resources Control Board has about 22 employees assigned to investigate suspected illegal diversions statewide. Wildlife officers often conduct their own investigations and refer illegal diversions to the water board for enforcement.
Since 2005, the water board has imposed fines or other corrective measures on property owners just 30 times for illegally diverting water or taking more than their share, according to a Sacramento Bee review of the agency's enforcement actions.
It has dozens more cases pending, but these can take years to work their way through the board's complex enforcement process.
Like most Western states, California adheres to a "first in time, first in right"principle of water rights. This means whoever first claimed water in a stream has a superior right to use that water.
The state retains authority over senior water-right holders to punish "waste and unreasonable use"of water, and to curtail their diversions during extreme drought years, but it has rarely done so.
"Part of the culture of the board is that they're not going to take away someone's water unless the evidence is pretty conclusive," said Chris Shutes, a water consultant who works with the California Sportfishing Protection Alliance and other groups to monitor illegal diversions.
The water board's enforcement staff responds to complaints and also looks for discrepancies in the required usage reports submitted by diverters.
Because of its limited staff, it is unable to conduct extensive field inspections.
But it does inspect individual watersheds to search for violations when possible, said John O'Hagan, manager of the water board's enforcement staff.
When it does go after illegal diverters, the board usually offers them a chance to settle their cases for fees well below the legal maximum. This avoids tying up staff in a long and complicated hearing process.
Holders of water-rights permits issued after 1914 are required to file annual reports with the board documenting their diversions. Senior water-rights holders are required to file similar reports every three years.
Not everyone complies: In the 2012-13 fiscal year, about 29% of those who were required to file water-use reports failed to do so. The board sent them warning notices and fined some who did not respond.
Even the reports that do get filed may not be very useful. Water use is entirely self-reported by the diverter. They may be using more or less than they are allowed, but there often is no way to know.
"We cannot verify whether something is accurately reported,"O'Hagan said. "We have nothing to base it against."
On March 1, Gov. Jerry Brown signed a new law that allows the board to order emergency curtailments on streams that risk running out of water. It also allows the board to skip some steps in the enforcement process, and jump straight to the cease-and-desist and penalty phases if the board believes a diverter is violating a curtailment order.
Finally, it doubles penalties for an illegal diversion to $1,000 per day, and adds a $2,500 per acre-foot penalty. Violating a cease-and-desist order gets even more painful, with penalties jumping from $1,000 to $10,000 per day.
These changes apply only during the present drought, not in other climatic conditions.
It remains to be seen, however, if the board has adequate staff to enforce broad curtailment orders this year.
The reporter can be reached at firstname.lastname@example.org or (916) 321-1264. Follow him on Twitter @matt_weiser.