Relative abundance trend of key non-native species, for example Brazilian waterweed (Egeria densa) and water hyacinth (Eichhornia crassipes), and harmful invasive species such as Microcystis aeruginosa and other harmful algal blooms (HAB).

Tons of industrial pollutants released and disposed of by watershed/region. Industrial waste may be released into waterways, soils, and the atmosphere. This may introduce chemicals into ecosystems, the air we breathe and the water we drink.

Percentage of irrigated lands that meet water quality standards in Delta Region

Correlation between quality and quantity of available drinking water and household income. Equitable access to clean, plentiful drinking water is considered to be a human and cultural right. Ensuring that this basic right is met is a societal responsibility and helps us to understand equity.

Rate of fertilizer applied per unit area (kg/ha). Fertilizer contains chemicals (e.g., forms of nitrate) that can harm aquatic ecosystems and degrade drinking water quality.

Groundwater describes water in soil and sub-soil substrates (e.g., aquifers) that is replenished across various time-frames by surface water that percolates to these underground reservoirs. For this water to be useable to meet human needs (e.g., drinking, irrigation) it must meet the same kinds of water quality requirements as surface water. One indicator of groundwater quality is nitrate concentration.

Groundwater water quality index. Because there are many possible contaminants that can affect the quality of drinking water, combining consideration of multiple indicators of quality into one index can help understand general groundwater quality.

California Communities Environmental Health Screening Tool ("CalEnviroScreen") is intended to support assessments of the potential environmental pollution effects on communities, including disadvantaged communities, in order to support reduction in disparities and threats to health. The groundwater component of CalEnviroScreen provides a relative ranking of communities' groundwater condition and so should not be considered an absolute indication of health risk or cumulative effects.

Proportion of watershed covered by impenetrable materials such as roads, parking lots, and buildings preventing water from leaching directly into the soil. Water quality is affected by impervious surface development in watersheds. The more impervious surfaces are developed, the greater the chance that water quality will be degraded.

Proportion of agricultural non-potable water needs--e.g. irrigation--met with non-potable water. The more non-potable water used for agriculture, the more potable water is available for drinking water and healthy aquatic ecosystems.