Why Is This Important?
High quality drinking water is essential to human health.  Contaminated water can cause acute dis­ease, birth defects, infant mortality, and increased cancer rates.  Federal and state safe drinking water regulations aim to assure the high quality of public water supplies.  Maximum Contaminant Levels (MCLs) are drinking water standards or limits of contaminants that are allowed in drinking water.  More stringent than MCLs, Action Levels are levels at which water managers must cut off any source of water leading to a drinking water use until remedial steps have been taken.

What Is a Sustainable State?
A sustainable state is one where drinking water is safe for all to drink.

How Are We Doing?
Three contaminants were chosen as indicators of drinking water quality: trihalomethanes, lead, and coliform.  Results are from the 2006 Annual Water Quality Reports from each water district.

Trihalomethanes
Trihalomethanes are byproducts of the disinfection process.  The health effects of trihalomethanes are unclear; studies have suggested associations with certain cancers, and reproductive and developmental defects, however.  The MCL for total trihalomethanes (TTHMs) is 80 parts per billion (ppb). 

  • All 20 water districts met state and federal standards for TTHMS, with average concentrations ranging from a low of 15.5 ppb in San Bruno to 72.3
    ppb in the Coastside County Water District.
  • In 2004, water districts switched from chlorine to chloramine for water disinfection.  In 2006, the average TTHM concentration of all water districts was 31 percent lower than in 2003, the last full year before the change.
  • Although the average reported by Coastside County was below state and federal standards, detected levels ranged from a low of 33 ppb to a high of 120 ppb.  The 120 ppb sample was detected at one site and the district is currently working to address the issue.  This was the only district to report detected levels above 80 ppb.

Data sources: 2006 Annual Water Quality reports from each water district

Lead
Lead can enter the water system from corruption of household plumbing systems.  Lead can hinder the physical or mental development of children and can cause adults to develop kidney problems or high blood pressure. 

  • All water districts reported that 90th percentile concentrations of lead were below the Action Levels of 15 ppb.  The 90th percentile concentrations ranged from zero to 7.8 ppb.
  • Eight of the 20 water districts had 90th percentile concentrations below two ppb.

Coliform bacteria
Coliform bacteria are naturally present in the environment.  The test for coliform bacteria serves as a general indicator for the presence of other bacteria, including harmful, disease causing bacteria.  The MCL for coliform is 5 percent positive for all test samples per month (or no more than one positive test per month for districts with fewer than 40 sample sites).

  • All water districts met state and federal standards for coliform bacteria.  Test results ranged from 0 to 2 percent positive per month.
  • Seventeen water districts reported detecting no coliform bacteria in their samples.

 

See appendix page 79, CLICK HERE. .  Researcher: Yi Tin Kao