Alert 9/30/22 | 5:06 PM: Santa Clara County reaches water savings goal in latest drought report. Learn more
Your Water
Ensuring safe, reliable water
Your Water
Page Title
Your Water
Back to top

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.


What are PFAS?

PFAS are a group of thousands of man-made chemicals that resist heat, oils, stains and water. They have been widely used in consumer products like nonstick cookware, carpets,  waterproofing clothing, furniture fabrics and food packaging. They are also 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. PFOA and PFOS are two common  PFAS chemicals.

What are the health effects of PFAS?

PFOA is a possible human carcinogen according to the International Agency for Research on Cancer. Studies suggest a certain level of PFAS exposure can cause adverse effects in humans, including increased cholesterol, thyroid and liver disease, decreased fertility, lower birth weights, decreased vaccine response and pregnancy-induced hypertension.

How are people exposed to PFAS?

These chemicals have been widely used for decades in industrial applications and consumer products. Most people have been exposed to PFAS through consumer products but drinking water can be an additional source of exposure. The major sources of PFAS in water supplies are fire training/response sites where 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?

No, but draft state and federal limits for PFOA and PFOS in drinking water are expected by late 2022. Lawmakers and regulators are moving toward stricter standards for the detection, public notification, and treatment of PFAS in drinking water.

The Environmental Protection Agency (EPA) recently released the following lifetime drinking water health advisories:

  • PFOA: 0.004 parts per trillion (ppt)
  • PFOS: 0.02 ppt
  • GenX: 10 ppt
  • PFBS: 2,000 ppt 

These health advisories are not enforceable but provide information for water providers. The advisories are conservatively based on lifetime exposure to PFAS in drinking water, also accounting for sensitive populations and potential PFAS sources beyond drinking water. If exceeded, EPA recommends water providers assess the contamination, inform customers, and limit exposure.

Previously, the State Water Resources Control Board (State Board) set drinking water notification levels for PFOA (5.1 ppt), PFOS (6.5 ppt), and PFBS (500 ppt). If exceeded, water providers must notify their governing bodies, and the State Board recommends they inform customers. The State Board set the current response level at 10 ppt for PFOA, 40 ppt for PFOS, and 5,000 ppt for PFBS. If exceeded, water providers are required to take the water source out of service, provide treatment, or notify customers in writing.

Has local water been tested for PFAS?

Yes, Valley Water and several local water retailers have tested various water sources. PFOA, PFOS, GenX, and PFBS have not been detected in Valley Water’s imported water or the treated water we supply to our retailers.

Valley Water has detected PFOA and PFOS below the State Board notification levels in two of the three water supply wells we own for emergency backup supply. No water from these wells has been delivered to water retailers or consumers. In 2020, Valley Water voluntarily sampled PFAS at 55 monitoring wells throughout Santa Clara County. These results and other available data indicate that PFOA, PFOS, and PFBS are not widely present in groundwater above the State Board notification and response levels.

Several local water retailers have tested their water supply wells for PFAS and most of them have found no detections. The main exception is one retailer who found PFOS above the State notification level in some water supply wells in San Jose and Campbell. The water retailer discontinued the use of the wells out of an abundance of caution and notified consumers. In Santa Clara County, PFOA or PFOS have not been detected in any water supply wells at levels where the State Board recommends removing the water source from service.

The State Board continues to order PFAS testing of wells throughout the state. Results from this testing, which includes wells in Santa Clara County, are helping us better understand the presence of PFAS in local groundwater.

How can PFAS in drinking water be treated?

Treatment technologies that have shown to be effective in removing PFAS from drinking water include granular activated carbon, powdered activated carbon, high-pressure membranes (reverse osmosis/nanofiltration) and ion exchange resin. More information can be found at and

Are PFAS found in bottled water?

Bottled water producers are not required to test for PFAS. 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 groundwater recharge or other uses. While PFAS are present in wastewater, any purified recycled water used in Santa Clara County would be treated with multiple, proven technologies including reverse osmosis, which is effective in removing 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 is protective of the environment.

What is Valley Water doing about PFAS?

Valley Water is concerned with any potential risks to safe drinking water and is committed to protecting public health.

Valley Water has been proactive in evaluating the threat posed by PFAS through voluntary sampling and coordination with other agencies. Our water quality laboratory is certified to test for PFAS in drinking water, but one challenge all water providers are facing is that the EPA health advisories are near zero. There are no EPA-approved testing methods that can detect PFAS to those low levels.

We take our responsibility to provide safe, clean water and to protect local groundwater very seriously. Valley Water and local 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 will continue to track the rapidly evolving PFAS science and regulations, work with our State and local regulatory agencies and water retailers, and provide timely, transparent communication to our customers and the public.

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.

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.

  • Document name guide
  • Notes: The browser IE 11 does not support the following search application. Please use Google Chrome or Microsoft Edge.

Search historic solvent case files


Related Files