Groundwater Quality | Santa Clara Valley Water
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Groundwater Quality


Most wells in Santa Clara County produce high-quality water that meets drinking water standards without the need for treatment. The primary exception is nitrate, which is elevated in a number of South County wells and continues to be a groundwater quality challenge. Cleanup is ongoing at a number of groundwater contamination sites and elevated levels of perchlorate are still observed in some South County wells. The district is working with other agencies, basin stakeholders, and the public to address these issues and ensure groundwater quality remains high.

The district monitors water quality at wells throughout the county and also evaluates data from local water suppliers to assess regional groundwater quality and identify potential threats so they can be appropriately addressed. The district also monitors the quality of water used for groundwater recharge to ensure groundwater resources are protected. The district's recent groundwater quality and recharge water quality information can be found in the reports below.

If your water comes from a public water supply, such a city or water company, it is tested regularly to make sure it meets state and federal drinking water standards. If your water comes from a private well, the district encourages you to have your well water tested annually by a certified laboratory to protect your health, even though your water may taste and look fine. More frequent testing is recommended if you notice a change in color, odor, or taste. The district's Guide for the Private Well Owner [PDF] offers helpful information on water quality testing, well maintenance and protection. The district is currently offering basic water quality testing for eligible private domestic wells and rebates for well owners exposed to high nitrate. For more information, please see the domestic well testing page or the nitrate treatment system rebate program page.

Leaking underground fuel tanks, industrial spills, storm runoff, septic systems, inefficient agricultural operations, and other sources can pollute groundwater, making it costly to treat or even unusable. Since the restoration of contaminated groundwater can take decades or longer, preventing contamination is critical. The district oversees well construction and destruction since improperly constructed or destroyed wells can allow contaminants to reach water supply aquifers. Other district efforts to prevent or mitigate contamination include technical studies, coordination with land use and regulatory agencies, and efforts to increase public awareness of the importance of protecting groundwater resources.

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 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, the water district 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 water district efforts include continued groundwater recharge (which helps to dilute nitrate), groundwater monitoring, public outreach, and collaboration with other agencies. The water district is also leading efforts to develop regional salt and nutrient management plans.

To reduce customer exposure to elevated nitrate, the water district is offering rebates for treatment systems for eligible domestic well users. See "What can I do if my well water is high in nitrate?" below for more information.

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. The water district 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 free water quality testing by the water district.

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 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 actually increase the nitrate concentration.

The water district is offering rebates up to $500 for eligible domestic well users that purchase and install treatment systems to reduce elevated nitrate. Visit our nitrate treatment system rebate page or call us at (408) 630-2300 for more information.

The State Division of Drinking Water maintains a list of certified residential treatment devices at Water treatment system vendors are also listed in the yellow pages under "Water Filtration & Purification Equipment." The water district recommends that you ask for assurance from the vendor or manufacturer that the system you are considering wil 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  

For general information on nitrate or groundwater quality, contact the district'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

Hard Water

What is it?

Hardness is a measure of dissolved minerals (usually calcium and magnesium) in water. As water comes into contact with soil and rock, it dissolves naturally-occurring minerals resulting in increased hardness. Hardness is measured in milligrams of calcium carbonate (CaC03) per liter (mg/L) or in grains per gallon. As shown below, water with hardness over 180 mg/L is considered very hard. The hardness in groundwater in Santa Clara County averages over 250 mg/L. By comparison, the average hardness of the District’s treated surface water is less than 120 mg/L.


Water Hardness Scale

mg/L Grains per gallon Classification  
Less than 60 Less than 3.5 Soft
60 - 120 3.5 - 7.0 Moderately Hard
120 - 180 7.0 - 10.5 Hard
Over 180 Over 10.5 Very Hard

What are the health effects?

Hard water does not pose a health risk, and there is no health-based drinking water standard. In fact, hard water may help you meet daily requirements for calcium and magnesium in your diet.

What problems are associated with hard water?
Although hardness does not affect the safety of your water, it can cause aesthetic issues. Hard water can affect the taste of your water and can be a nuisance for cleaning tasks. The taste is sometimes described as metallic or medicinal because of naturally occurring iron and minerals in the groundwater. Hard water deposits may build up on dishes, glasses, plumbing fixtures, and wash basins, and hardness may cause poor soap and detergent performance. Hard water can also cause the build-up of scale on pipes and fixtures that can eventually lead to lower water pressure and reduced efficiency of water heaters.

How do I test for hardness?
If your water comes from a public water supply, such as a city or a water company, your water is regularly tested for hardness and many other substances. Each year, retail water providers publish a water quality report to show consumers exactly what is in the water they provide.

If your water comes from a domestic well, you may be eligible for free basic water quality testing by the water district, including testing of water hardness. Contact the water district’s Groundwater Hotline at (408) 630-2300 for more information.

If you want to test your water for hardness, the water district recommends that you use a state-certified laboratory.

How can I treat it in my water?
Hardness does not pose a health hazard, but if you want to reduce the hardness of your water for aesthetic reasons, you can install a water softener or ion exchange system. These systems can increase the sodium content of your water, which may pose health concerns for your household. These systems may also contribute additional salts to wastewater treatment plants and ultimately to recycled water, which is reused for other purposes. If you want to avoid the use of water softeners or ion exchange systems for health or environmental reasons, there are cleaning products and natural remedies (such as vinegar) that will help to address mineral build-up caused by hard water.


One of the primary goals of the Santa Clara Valley Water District is to protect local groundwater resources. In 2003, an investigation performed under the direction of state water officials detected the chemical perchlorate in water wells in Morgan Hill, San Martin, and Gilroy. The Central Coast Regional Water Quality Control Board has regulatory oversight over the cleanup of the groundwater plume, which extends approximately ten miles. The district continues to work with the Regional Board and the local community to ensure the contamination is adequately addressed.

The State Water Resources Control Board's Geo Tracker website contains the most current information on the Olin case, Including monitoring reports, cleanup progress reports, and correspondence.

Fuel Leaks and Solvents

Leaking underground storage tanks

Oversight responsibility for investigations and clean-up of releases from underground storage tanks was transferred from the Santa Clara Valley Water District to the Santa Clara County Department of Environmental Health as of July 1, 2004.  DEH files on leaking underground storage tanks have been transferred to the State Water Resources Control Board's GeoTracker database.  For more information, see the County's file review page.

Solvent and toxic release cases

Solvent and toxic release sites in Santa Clara County are primarily regulated by the following Agencies:

The Santa Clara Valley Water District provides peer review to regulatory agencies on hazardous material release cases that pose the greatest threat to groundwater resources.

View historic solvent case files

Some historic solvent case files are available online. Please note, these files are not maintained by the district. For complete case files, including the most recently submitted reports, contact the regulatory agency overseeing the case. Use the search tool at the bottom of this page to view historic files. If you have questions, please contact George Cook at (408) 630-2964 or submit a Public Records request.

Select a field and enter your search terms, then click Start Search: