All is not well in Hillsborough, a suburb of 11,500 people west of San Mateo that's among the nation's wealthiest towns. There, nine unhappy residents are suing the municipality to recoup fines that were temporarily enacted to encourage conservation in light of the ongoing California drought.

Now, before you weep for these would-be water rights advocates, know that they probably don't need the additional moisture: Hillsborough homes, which cost an average of $4.3 million, typically use three times as much water as elsewhere. But Beau Burbidge, an attorney who represents the aggrieved residents, argues in the San Mateo County Superior Court lawsuit that the temporary town-imposed fines, put in place to promote state-directed cutbacks, were unconstitutional. “We understand the drought is severe and water use needs to be cut,” Burbidge tells the Chronicle, who covered the story. “But we have to do that in a matter that’s consistent with the law,” he insisted.

Who are Burbidge's clients? “A lot of them are top-tier users,” he tells the Mercury News. “They have quite a bit of acreage. They all let their lawns go brown. They put in drought-friendly plantings, and all they did was get penalized.”

The State Water Resources Control Board called for California-wide water restrictions in 2015, and those were in effect through this past summer, when they were lifted. Under those restrictions, Hillsborough was directed to cut back its water consumption by 36 percent over its 2013 rate or else face state penalties — it did so successfully, though it still uses three times as much water as the average town.

In response to the demands of the state, on top of tiered pricing, the town began to impose fines for excessive water use beginning last summer. Local consumers were allotted a certain amount of water based on their parcel and household and were charged an extra $30 for every 748 gallons by which they exceeded it. That netted the town $600,000 before the system was dropped after the state restrictions were lifted.

But penny-pinching town residents aren't going to let those fines just go down the drain. "It’s about the principle," Burbidge tells the Mercury News. "It’s not like the clients are becoming destitute from the water rates, but the town is running amok.”

Burbidge, who represents venture capitalist David Marquardt, wealth manager Eldridge Gray, oral surgeon Charles Syers, and six others in their fight, argues that based on voter approved California Proposition 218, the fines were illegally imposed in the first place. The argument follows the logic of a case from the Orange County city San Juan Capistrano, which is based on the proposition's pronouncement that public agencies can't charge more for a service than what it costs to provide the service.

“All they’re really doing is charging extra for extra water use,” Burbidge tells the Chronicle. Since the town of Hillsborough buys its water at a fixed cost from the SFPUC, his lawsuit claims that fines like those imposed are unconstitutional.

Lawyers for Hillsborough reject that claim, countering that the fines are legit because the cost of delivering the water, not buying it, goes up with consumption.

Michael Lauffer, chief counsel for the State Water Resources Control Board, also contends that Prop. 218 applies to property-related fees but not to civil fines, but that's led Burbidge to argue that the Hillsborough fines are just fees.

If the small group of Hillsborough residents are successful in their lawsuit, it's bad news for California towns that might similarly hope to promote conservation with fines. "Until we get a good court decision from the Supreme Court or other courts of appeal, it makes it difficult to actually advance the law in this area,” Lauffer told the Chronicle.

Of course, not everyone is horrible. Paul Saffo, a Hillsborough resident, puts it simply to the Merc: “We’re in a drought... We have a short reprieve, but the fact is that this problem is only going to get worse, long term, and everybody has to pull together.” If the court strikes down Hillsborough's enforcement measure, he and others who use less water than the area's biggest users will pay a greater share of the bill.

Related: California Lifts Mandatory Water Restrictions Though Drought Continues