If regional water agreements were easy to craft, we'd have more of them in the Sacramento area. They aren't easy. They require trust and sacrifices. That's why a proposed water-sharing pact between Woodland and Davis has become so contentious, particularly in Davis.

Through mail-in ballots due by March 5, voters in that city are now deciding on Measure I, which asks if Davis should proceed with a Sacramento River water project with Woodland, subject to adoption of water rates under Proposition 218.

The goal of the project is to improve water quality and reduce Woodland's and Davis' dependence on uncertain groundwater supplies. High in salts and metals such as selenium, that groundwater creates challenges for both cities in providing drinking water and disposing of treated wastewater under increasingly stringent state standards.

If the project were relatively cheap, this choice would be an easy one for Davis voters. It's not. Water rates for a typical Davis household are expected to triple over five years to pay for the city's share of a project slated to cost (in 2012 dollars) roughly $245 million.

While Woodland has raised rates to put aside money for this project, Davis has dithered, one reason that at least some of its residents are having sticker shock.

Opponents of Measure I say it is all unnecessary. They say there no need for Davis to quickly transition from groundwater. They say that regulators are unlikely to crack down on Woodland and Davis for continuing to release wastewater high in salts and heavy metals. They say that Davis could easily team up with West Sacramento on a water-sharing arrangement instead of working with Woodland and Conaway Ranch on a screened diversion from the Sacramento River.

True, Davis could probably take several years to get serious about protecting its aquifers, but at what cost? Currently, the city is playing triage with its groundwater supply, drilling new wells to deal with supply and contamination problems. It has drilled deep wells, and could drill more. Yet that's a risky policy. As Graham Fogg, a UC Davis hydrologist has noted, "The capacity of the deep aquifer to satisfy city water demand is unknown at this time because there is not yet enough information on the lateral extent of that aquifer and on how and at what rate it is recharged."

Will regulators really crack down if the Woodland-Davis project falls apart? Maybe not, but remember that Sacramento once gambled and lost. The result was an order by the Central Valley Water Quality Control Board that could cost the Sacramento Regional County Sanitation District more than $1 billion in treatment upgrades.

Could Davis team up with West Sacramento? Perhaps, but it would likely be under West Sacramento's terms – making Davis a water customer, not a partner. That might be cheaper for Davis in the short run, but not necessarily in the long run.

Known for their strong environmental sensibilities, most Davis residents realize they have to pay more if they want to create a more sustainable water supply. Currently, at an average of $34 per month, Yolo County households pay less for their water than their counterparts in Sacramento, Placer and Solano counties, according to a recent survey for the California-Nevada section of the American Water Works Association.

While critics can find fault in both the process and projected costs of the Woodland-Davis project, they have to ask themselves: Are they really so sure their alternatives are viable? And is the city willing to shoulder the consequences if they aren't?

Davis voters unwilling to take such risks should vote "Yes" on Measure I.

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