Editor's note: Whether it's working toward a solution in the Bay/Delta, advocating the clean-up of toxic waste in Moab, Utah, or funding desalination research, Metropolitan commits a significant amount of effort and resources to protect water quality.

As part of our continuing effort to examine important water issues, this issue features a trio of stories about how Metropolitan keeps water safe.

Writers Joe Pomento and Denis Wolcott examine salinity, one of the most insidious and expensive water quality problems we face in Southern California. Debra Sass explains how the U.S. Environmental Protection Agency and the California Department of Health Services use a complex set of rules and rationale in setting health standards for contaminants, such as arsenic. And Gigi Hanna interviews several scuba divers who spend their days underwater to keep Metropolitan's system of pipes, canals, siphons and reservoirs working smoothly and the water free of taste and odor problems.