Excess salinity poses a growing threat to food production, drinking water quality and public health. Salts increase the cost of urban drinking water and wastewater treatment, which are paid for by residents and businesses. Increasing salinity is likely the largest long-term chronic water quality impairment to surface and groundwater in the Central Valley. Salinity, including nitrate, from past and current sources impair beneficial uses of waters throughout the Valley landscape and result in pollution of drinking water sources for some communities in the Central Valley.
The United States Geological Survey (USGS) classifies water of varying concentrations of salt as:
- Freshwater: Less than 1,000 parts per million (ppm)
- Slightly saline water: 1,000 ppm – 3,000 ppm
- Moderately saline water: 3,000 ppm – 10,000 ppm
- Highly saline water: 10,000 ppm – 35,000 ppm
Seawater is about 35,000 ppm salt. Salt enters waterways from contact with rocks containing soluble minerals, which is how even “fresh” water far from oceans can become especially salty. This is particularly true for groundwater, which can continue to move between mineral-containing rocks for thousands of years and accumulate tremendous concentrations of salt. However, inadequate removal of vegetation, improper land use, industry and irrigation can bring salty groundwater much closer to the surface.
Sodium and potassium have a unique relationship that allows their proper balance to remove the body’s undesired fluids from the bloodstream. From there it reaches the kidneys for further processing into what will eventually become urea, excreted as urine and removed from the body. When too much salt is ingested, the harmony between sodium and potassium levels is disrupted and the kidneys are unable to eliminate enough water from the bloodstream. Kidneys become overwhelmed, leading to irreparable damage, including kidney stones and failure altogether. Additionally, unremoved fluid builds up to cause high blood pressure and heart problems.
Saline water stunts plant growth by dehydration, preventing nitrogen uptake and poisoning with chloride ions. In freshwater, salt damages the health of plants and aquatic life, putting species at risk.
Salinity promotes the accumulation of suspended particles (like clay) into larger chunks, allowing an unnatural amount of sunlight to infiltrate. This could scorch native plant species and encourage the proliferation of toxic, parasitic or highly competitive algae. Additionally, when salty waters contaminate soil, its structure and integrity is degraded, allowing for erosion.
According to the United Nations University’s Institute for Water, Environment and Health, excessively salty soils exacerbate global warming by prompting the emissions of more greenhouse gases.
Salty water is not good for crops such as carrots, beans, avocados and strawberries, which are particularly intolerant to salt. Deterioration of soil leads to damaged infrastructure, loss of productive farmland and reduced crop yields.
More than 2,000 hectares (approximately 3,000 football fields) of irrigated farmland are lost daily due to salt damage, costing more than $27 billion in lost crops annually. To reverse these effects, farmers may plant trees, plow deeper, harvest salt-tolerant crops, mix harvested plant residues into topsoil or dig drains around salt-affected areas.
Salinity in California’s Water
Salinity is enhanced in dry climates, owing to a lack of rainfall to rinse away any salt deposited from evaporation or transpiration. In addition to salinification of groundwater through long-term contact with underground rocks and minerals, California’s water supply gains salt through use of water softeners and from seawater intrusion. To eliminate hard water and its resulting clogging of pipes, water softeners exchange magnesium and calcium with sodium or potassium, a process requiring a highly saline fluid that is ultimately deposited in sewers or leachfields for subsequent contamination.
Overpumping of groundwater leads to intrusion of seawater into freshwater aquifers, extreme examples of which include the Salinas Valley, Santa Clara Valley and Los Angeles County groundwater basins. Subsurface barriers and injection wells have been employed to enhance the quality of these drinking water aquifers. The former is a temporary remedy requiring inserting impermeable grout below the ground’s surface at sites with a risk of leaching salts (and other contaminants) to prevent them from seeping through to groundwater. Injection wells are drilled reservoirs for unwanted fluids and gases, in this case for saltwater, guarded by clay and rock below the lowest source of drinking water.