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Groundwater Quality


Most wells in Santa Clara County produce high-quality water that meets drinking water standards without any treatment. However, elevated nitrate and perchlorate are found in some South County wells. Valley Water continues to work to protect groundwater quality and to advocate for effective remediation.

By monitoring water quality throughout the county and evaluating data from local water suppliers, Valley Water assesses regional groundwater quality and identifies potential threats so they can be appropriately addressed. Recent groundwater 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, Valley Water encourages you to:

Leaking underground tanks, industrial spills, septic systems, inefficient agriculture, and other sources can pollute groundwater, making it costly to treat or even unusable. Remediation can take decades or longer, so preventing contamination is critical. Valley Water oversees well construction and destruction since improperly constructed or destroyed wells can allow contaminants to reach water supply aquifers. Other efforts to prevent or mitigate contamination include technical studies, coordination with land use and regulatory agencies, and efforts to increase public awareness.


Protecting public health and the quality of your drinking water is our top priority. Valley Water continues to track the rapidly evolving science and regulatory developments related to per - and poly-fluoroalkyl substances (PFAS) and to evaluate potential impacts on local water supplies.

What are PFAS?

PFAS are a group of thousands of human-made chemicals that resist heat, oils, stains and water. They have been widely used in consumer products like nonstick cookware, stain resistant carpets and fabrics, waterproofing clothing, and food packaging. They have also been used in industrial processes and firefighting foams. PFAS are often called “forever chemicals” because they break down very slowly and can accumulate in humans, animals and the environment. PFAS have been found in water, air, and soil worldwide. PFOA and PFOS are two common PFAS chemicals.

What are the health effects of PFAS?

A wide range of scientific studies suggest a certain level of PFAS exposure can cause adverse health effects in humans, including reproductive and developmental effects, increased risk of cancer, increased cholesterol, reduced immunity, decreased vaccine effectiveness, interference with natural hormones, and liver damage.

How are people exposed to PFAS?

Most people have been exposed to PFAS through consumer products, but drinking water can be another exposure source. The major sources of PFAS in water supplies are fire training and response sites where fire-suppressing foam was applied, industrial sites, landfills, and wastewater treatment plants/biosolids. Because of their persistence in the environment, PFAS can accumulate in water supplies.

Are there limits for PFAS in drinking water?

Yes, on April 10, 2024, the U.S. Environmental Protection Agency (EPA) established a Maximum Contaminant Level (MCL) of 4 parts per trillion (ppt) for PFOA and PFOS and 10 ppt for PFNA, PFHxS, and GenX. The rule also regulates combined amounts of four other types of PFAS chemicals (PFNA, PFHxS, PFBS, and GenX).

Public water systems will need to monitor their water supply for these chemicals within three years and include the results in their Annual Water Quality Reports to customers. Systems that detect PFAS above the drinking water limits will have up to five years to implement solutions, such as treatment or other actions, to ensure water delivered to customers does not exceed these limits. Water systems must also notify the public if levels of regulated PFAS exceed these new standards. For more information, please visit

Has local drinking water been tested for PFAS?

Yes. Valley Water’s treated water supplies meet the drinking water regulations as none of the six PFAS have been detected. This means that all the water supplied by Valley Water’s three treatment plants to water retailers continues to meet all federal and state regulatory requirements, including the PFAS drinking water limits, and is safe to drink.

PFOA and PFOS have been detected at and just above the MCL in two of three wells in Valley Water’s Campbell Well Field. However, water from these emergency supply wells has never been served to water retailers or the public. Some water retailer wells are expected to be impacted by the EPA rule, which could require treatment or other actions.

The State Board and EPA continue to order PFAS testing of water supply wells throughout the state. Related results from wells in Santa Clara County are helping us better understand the presence of PFAS in local groundwater.

What if I have a private well?

Unlike public water systems, water from domestic wells is not subject to federal or state water quality regulations. To protect your health, you may want to test your drinking water for PFAS and other potential contaminants. Valley Water recommends using an accredited laboratory to test your drinking water.

How can PFAS in drinking water be treated?

Some public water systems may need to treat their source water to ensure water delivered to customers meets drinking water limits. Various treatment technologies can reduce PFAS, including activated carbon, reverse osmosis, and ion exchange.

If you are concerned with PFAS in your water, please contact your water provider for information on whether PFAS are present in the water delivered to your area. If you are interested in a home treatment system, PFAS can be reduced by certain filters installed on faucets, whole-house systems, or pitcher-type filters. If considering a home treatment system to reduce PFAS:

  • Check the product packaging or specifications for NSF/ANSI 53 or NSF/ANSI 58 certification to reduce PFAS.
  • Confirm this certification through a reputable, independent testing agency like NSF (see link below).
  • Follow the manufacturer’s instructions for maintenance and filter replacement. Proper maintenance is essential to ensure the system reduces PFAS as designed.

More information on PFAS treatment options can be found at:

 Are PFAS found in bottled water?

Bottled water producers are not subject to EPA drinking water regulations. The Food and Drug Administration, which regulates bottled water, evaluates EPA drinking water standards and adopts bottled water standards as appropriate. There are currently no federal regulations for PFAS in bottled water. We recommend consumers contact bottled water producers directly for information about their product’s water quality.

Are PFAS found in purified recycled water?

Valley Water is exploring the use of purified recycled water as a drought-resilient water supply for drinking water purposes. While PFAS may be present in wastewater, any purified recycled water used by Valley Water would be treated with multiple proven technologies, including reverse osmosis, which effectively removes PFAS. Valley Water is carefully testing these technologies at our Silicon Valley Advanced Water Purification Center to ensure purified recycled water meets or exceeds drinking water standards and protects human health and the environment.

What is Valley Water doing about PFAS?

We take our responsibility to provide safe, clean water and to protect groundwater very seriously. Valley Water has been proactively evaluating the threat posed by PFAS through voluntary sampling and coordination with other agencies. Our water quality laboratory is accredited to test for PFAS in drinking water.

Valley Water and our water retailers use proven technologies and best practices to ensure drinking water delivered to businesses and residents meets or exceeds all drinking water standards. Valley Water continues to collaborate with regulatory agencies and water retailers to assess impacts to local supplies and to evaluate potential sources and treatment technologies. Valley Water will also continue to provide timely, transparent communication to customers and the public.


To find out more about PFAS or to submit questions or comments, please contact Vanessa De La Piedra at (408) 630-2788 or [email protected].

  • Download a pdf version of this fact sheet link
  • For information on PFAS in Groundwater please see this link

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,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.


What is chromium-6? 
Chromium-6, or hexavalent chromium, is a naturally occurring metal. It is also used in several industrial processes. There are other forms of chromium such as chromium-3, which is an essential nutrient and is sold as a dietary supplement. 

What are the health effects of chromium-6? 
Chromium-6 has been known to cause cancer in humans when inhaled. In scientific studies in laboratory animals, chromium-6 has also been linked to cancer when ingested. 

How does chromium-6 get into water supplies? 
Chromium-6 can occur naturally so it may be present in some groundwater aquifers. The types of rocks and soil associated with chromium-6 are known to occur in parts of Santa Clara County. Chromium-6 can also reach water supplies from industrial uses such as stainless-steel production, metal plating, and leather tanning. 

Is there a drinking water standard for chromium-6? 
No, but state limits on chromium-6 are expected by 2024. The State Water Resources Control Board (State Board) is considering a maximum contaminant level (MCL) of 10 parts per billion (ppb). One part per billion is equivalent to one drop of water in an Olympic size (660,000 gallon) swimming pool. MCLs are designed to protect public health and be feasible for water agencies to achieve.

The State Board has an MCL of 50 ppb for total chromium. This enforceable standard, which is more stringent than the federal limit of 100 ppb, remains in effect for drinking water. When an MCL is adopted for chromium-6, it will also be an enforceable regulatory standard that must be met by all public water systems. 

Has local water been tested for chromium-6? 
Valley Water has tested water from our three drinking water treatment plants, and has never detected chromium-6 at or above 1 ppb. This is the lowest reporting level currently available for a state accredited laboratory. 

Because it occurs naturally in soil and rock, chromium-6 is found more often in groundwater than in surface water. Chromium-6 has been tested at over 250 public water supply wells in Santa Clara County and was below the proposed 10 ppb drinking water limit in 99% of wells. Chromium-6 results ranged from non-detect to 19 ppb, and the median level was 2 ppb.

How do I know if my water contains chromium-6? 
Public water systems throughout the state have tested for chromium-6. If you get your water from a water company or city, they can provide you with the best information on the quality of water delivered to you. You can find contact information for your water retailer at If your water comes from a private domestic well, you may want to test your water for chromium-6. Valley Water recommends using a laboratory certified to test drinking water. A list of local certified laboratories is available at

Is there a filter that will reduce chromium-6? 
Yes, treatment technologies such as reverse osmosis can reduce or remove chromium-6. The State Board provides information on home treatment devices at

Valley Water recommends that you talk to the manufacturer or the company installing the system to confirm it will meet your needs. 

Is this the chemical that was the subject of the movie, “Erin Brockovich”? 
Yes. However, the maximum level detected in Santa Clara County is thousands of times lower than levels detected due to industrial contamination in Hinkley, California (the subject of the movie).

Is chromium-6 found in bottled water? 
Bottled water producers are not required to test for chromium-6. Valley Water recommends consumers contact bottled water producers directly for information about their product’s water quality. 

What is Valley Water doing about chromium-6? 
We take our responsibility to provide safe, clean water and to protect local groundwater very seriously. Valley Water and our water retailers use proven technologies and best practices to ensure drinking water delivered to residents and businesses meets or exceeds all drinking water standards. We will continue to track the science and regulations for chromium-6, and provide timely, transparent accurate information communication to our customers and the public. 


To find out more about chromium-6, please contact Geoff Tick at 408 630-2060 or [email protected].  


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 submit a Public Records request.

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