Poor water quality is expensive.

The Contra Costa Water District has spent about $850 million in the past 10 years on capital improvements, and most of that was to deal with the salt and organic compounds in its sole source of water, the Delta.

More than half, $450 million, was used to build Los Vaqueros Reservoir, which was intended to capture high-quality water in the spring for use later in the year, when the Delta gets saltier.

To deal with salt and carbon, the water district can change its intakes or use more water from Los Vaqueros.

But once in the treatment plants, managers face a difficult set of regulations that require them to thoroughly disinfect the water for its 500,000 customers while at the same time maintaining low levels of the hazardous byproducts created during disinfection.

Treating water that contains organic compounds and bromides can lead to hazardous byproducts such as bromate and trihalomethanes. Use too little disinfection, and you risk sending out unhealthy bacteria. Use too much, and you risk sending out too many byproducts.

"It (poor water quality) complicates the disinfection process," said Greg Gartrell, Contra Costa Water District assistant general manager.

The water district, which meets all safe drinking water standards, has cut its use of chlorine and now uses more ozone to treat bacteria. That reduces formation of trihalomethanes but increases formation of bromates.

In October, the water district received a patent for a new water treatment method that uses chlorine dioxide and ozone to reduce the amount of ozone used and the amount of bromate produced.

It allows other water districts to use the patented method without restrictions.

The water district is the most insistent in the state in trying to force improvements to water quality in the Delta itself.

"The only drinking water standard in the Delta relates to taste," said Gartrell. That standard regulates chlorides, another kind of salt.

Last year, CalFed and the Central Valley Regional Water Quality Control Board agreed to develop a drinking water policy for the Delta that could allow, or require, the state to regulate pollution discharges and water operations to make sure the state's single most important source of drinking water can meet standards for other contaminants.

Mike Taugher covers natural resources. Reach him at 925-943-8257 or mtaugher@cctimes.com.