Water rates are set to continue their seemingly inexorable rise in Santa Rosa and many nearby communities this year with the Sonoma County Water Agency proposing to charge cities more for the water they buy from the agency.

To raise money for planned upgrades to its system, the agency is proposing to raise its wholesale water rates — the price it charges cities and water districts in Sonoma and Marin counties for water — by 5 percent starting July 1.

Under the plan, the wholesale price of water would increase from $672 per acre-foot of water to $705.

Costs to users will go at a lesser rate. Santa Rosa officials expect the city water rates to increase 2.1 percent when the higher water costs are passed on, said David Guhin, director of the city utilities department.

That's in addition to the 2 to 5 percent increases in the combined water and sewer bills that went into effect 2012 and 2013.

The latest mid-year increase is no surprise. Three years ago the city switched to a system in which it passes any increase in the wholesale cost of water onto ratepayers when the increases occur July 1. Prior to that the city absorbed the higher water costs until water and sewer rates were reset, which happens every two years.

The mid-year increases over the last three years have been between two and three percent.

But in Santa Rosa, where water and sewer rates have more than doubled in the past decade, any increase in utility rates is closely scrutinized by users.

Last month county water officials outlined for the city's Board of Public Utilities some of the reasons for the increases. Among those are several upcoming infrastructure projects.

One is replacing the fish screen and fish ladder to improve the ability of young salmon to survive the agency's water diversion system at its inflatable dam on the Russian River at Mirabel. The costs are estimated at $3 million to $4 million.

Another project involves seismic upgrades to the pipeline beneath Sonoma Avenue, a project that will cost $3.2 million and is expected to get underway soon.

The third and potentially most expensive project is for habitat improvements to protect young fish in Dry Creek from the powerful discharges from Lake Sonoma. If efforts now underway to make the creek safer don't work, the agency could be required to stop releasing water into the creek from Warm Springs Dam, and instead build a pipeline at a cost of up to $140 million.

Depending on the solution, water agency officials said they expect wholesale water prices will need to increase 5 to 6 percent per year for the next five years to cover the costs of habitat improvements in Dry Creek, which are the result of 2008 study by the National Marine Fisheries Service.

Guhin said raising prices now in preparation for future projects will reduce the amount the agency will need to borrow to complete the work, and thus reduce the costs.

The Board of Public Utilities has recommended the City Council accept the price increase. The Council will consider the issue Tuesday, and must decide whether to sign off on the increase.

(Contact Staff Writer Kevin McCallum at 521-5207 or kevn.mccallum@pressdemocrat.com.)