Nitrate in Groundwater

What is nitrate?
Nitrate is formed in the soil when nitrogen and oxygen combine. Fertilizers, septic systems, and livestock waste contribute additional nitrate, so elevated nitrate is most often found in rural and agricultural areas. Since the Santa Clara Valley has a long history of agricultural production and septic systems are still in use in some areas, nitrate is an ongoing groundwater protection challenge, particularly in South County.

How does nitrate get into my well water?
Nitrate travels easily through the soil, carried by rain or irrigation water into groundwater supplies. Wells that tap groundwater may be affected. Shallow wells, wells near a source, wells in sandy soil, or wells that are improperly constructed or maintained are more likely to have nitrate contamination.

Does nitrate pose a health risk?
Nitrate can interfere with the blood's ability to transport oxygen, causing a condition called methemoglobinemia. It is of greatest concern for infants and pregnant women, and the effects of nitrate are often referred to as "blue baby syndrome." For more information on the health effects of nitrate, please see the State Division of Drinking Water website at https://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/Nitrate.html or consult your health care provider.

What is the safe level of nitrate in drinking water?
Nitrate is a regulated drinking water contaminant in California. The maximum contaminant level is 45 milligrams per liter (mg/L) for nitrate as nitrate (NO3) or 10 mg/L for nitrate as nitrogen (N). Public water systems are required to monitor water quality and take action to ensure water delivered to consumers meets drinking water standards for all regulated contaminants, including nitrate.

What is the Santa Clara Valley Water District doing about nitrate?
Since the 1990s,Valley Water has implemented many programs and worked with stakeholders and other agencies to:

define the extent and severity of nitrate contamination,
identify potential sources of nitrate,
reduce nitrate loading to groundwater, and
reduce customer exposure to elevated nitrate.

Current Valley Water efforts include continued groundwater recharge (which helps to dilute nitrate), groundwater monitoring, public outreach, and collaboration with other agencies. Valley Water also led efforts to develop regional salt and nutrient management plans.

Do I need to test my water for nitrate?
If your water comes from a public water supply, such as a city or water company, it is tested regularly to ensure that it meets drinking water standards. Contact the agency that provides your water bill to get more information on water quality, including nitrate.

If your water comes from a domestic well, you are responsible for ensuring that it is safe to drink. Because nitrate is colorless and odorless, the surest way to tell if you have nitrate in your water is to have it tested. Valley Water encourages domestic wells owners to have their well water tested annually by a local state-certified laboratory. Testing should be more frequent if there is a change in the water taste, odor, or appearance. Domestic well owners may be eligible for Valley Water. Visit the domestic well testing web page or call us at (408) 630-2300

What do the results of my water test mean?
Lab results should be interpreted carefully since nitrate can be measured as NO3 (nitrate) or as N (nitrogen). The state drinking water standard for nitrate as NO3 is 45 mg/L. This is equivalent to 10 mg/L for nitrate as N. Results above these standards would require action by a public drinking water system, such as blending or treatment. Although domestic wells are not subject to drinking water standards, these standards provide context to help interpret the results of your water test.

What can I do if my well water is high in nitrate?
If the level of nitrate in your water is higher than the drinking water standard, you may want to consider installing a water treatment system or using an alternate source of water for drinking, cooking, and mixing baby formula. Boiling the water does not remove nitrate but may instead increase the nitrate concentration.

The State Division of Drinking Water maintains a list of residential water treatment systems certified to reduce nitrate. These systems are typically installed under the kitchen sink and many can be purchased for less than $750. You can also contact a water treatment system vendor for further assistance. Valley Water recommends you ask for assurance from the vendor or manufacturer that the water treatment system you are considering will work for your situation.

How can I guard against nitrate in my water?
Fertilizer, septic systems, and animal waste and are all potential sources of nitrate contamination. The following guidelines will help to reduce the risk of nitrate contamination:

Ensure proper well location, construction, and maintenance: Wells should be located uphill (upgradient) and at least 100 feet away from septic tanks, leach fields, animal confinement areas, and fertilized areas. The well casing should extend above the ground and surface runoff should be directed away from the wellhead. The concrete slab on the wellhead should be intact.
Perform proper septic system maintenance: To help avoid system failure that can lead to contamination and the need for costly repairs, maintain your system according to the specifications and consider the tips below:

o Don’t drive or park heavy equipment over your septic tank, drain pipes or leach field.
o Avoid planting trees or shrubs near drain pipes or the leach field as roots can clog the lines.
o Don't dispose of hazardous chemicals or non-biodegradable materials in your toilet or drain.
o Install a lint trap on your washing machine.
o Conserve water.
o Have your septic tank inspected and pumped every three to five years (more often if you have a garbage disposal).
o If you have two leach fields, switch them every year.
Reduce your fertilizer use: Use fertilizers only when necessary, and according to the manufacturer's instructions.

For more information

Valley Water’s “Guide for the Private Well Owner” offers helpful information on water quality testing, well maintenance, and groundwater protection.

For general information on nitrate or groundwater quality, contact the Valley Water’s Groundwater Hotline at (408) 630-2300.

For information on well treatment or septic system operation, contact the Santa Clara County Department of Environmental Health at (408) 918-3400.