Nitrate—the oxidized form of dissolved nitrogen— is the main
source of nitrogen for plants. It occurs naturally in soil and
dissipates when the soil is extensively farmed. Thus, nitrogen
fertilizers are applied to replenish the soil. However, these
nitrates can be toxic, especially when they enter the food chain
via groundwater and surface water.
Stormwater runoff has emerged as a primary water quality issue.
In urban areas, after long dry periods rainwater runoff can
contain accumulations of pollutants. Stormwater does not go into
the sewer. Instead, pollutants can be flushed into waterways with
detrimental effects on the environment and water quality.
Water containing wastes – aka wastewater – from residential,
commercial and industrial processes requires treatment to remove
pollutants prior to discharge. After treatment, the water is
suitable for nonconsumption (nonpotable) and even potable use.
Water quality in California is regulated by several state
agencies, including the State Water Resources Control Board
(State Water Board) and its nine regional boards, which
enforce clean water laws and the Department of Public Health.
Water quality concerns are also often involved in disputes
over water rights, particularly in situations involving
endangered species or habitat.