We encourage you to review this annual water quality report, also called your Consumer Confidence Report, as it details any constituents detected in your water supply in 2018 and shows how your water compares to federal and state standards.
If you have any questions, please Contact Us. We are here to assist you.
Your Water System
District: Los Altos
System: Los Altos
System ID: #4310001
Cal Water has provided high-quality water utility services in the Los Altos area since 1931. To meet the needs of our customers in Los Altos and parts of Los Altos Hills, Cupertino, Mountain View, and Sunnyvale, we use a combination of local groundwater and purchased water. Our purchased water, which is treated surface water from the Santa Clara Valley Water District (SCVWD), comes from SCVWD reservoirs and the San Joaquin-Sacramento River Delta.
Our water system includes 297 miles of main, 65 booster pumps, and 46 storage tanks.
Cal Water's company-wide water quality assurance program includes vigilant monitoring throughout our systems and testing at our state-of-the-art laboratory. Additionally, we proactively maintain and upgrade our facilities to ensure a reliable, high-quality supply.
If you have any questions, suggestions, or concerns, please contact our local Customer Center, either by phone at (650) 917-0152 or through the Contact Us page.
By the end of 2002, Cal Water had submitted to the Division of Drinking Water (DDW) a Drinking Water Source Assessment and Protection Program (DWSAPP) report for each water source in the water system. The DWSAPP report identifies possible sources of contamination to aid in prioritizing cleanup and pollution prevention efforts.
The water sources in your district are considered most vulnerable to the following activities, for which no associated contaminant has been detected:
- Sewer collection systems
- Gas stations
- Dry cleaners
- Underground storage tanks (confirmed leaking tanks)
- Chemical/petroleum pipelines
- Electrical/electronic manufacturing
- Research laboratories
- Agricultural drainage
- Wells (agricultural)
SCVWD provides treated surface water to the Silicon Valley from three water treatment plants. SCVWD surface water is mainly imported from the South Bay Aqueduct, Lake Del Valle, and San Luis Reservoir, which all draw water from the Sacramento-San Joaquin Delta watershed. SCVWD's local water sources include Anderson and Calero Reservoirs.
SCVWD's source waters are vulnerable to potential contamination from a variety of land-use practices, such as:
- Agricultural and urban runoff
- Recreational activities
- Livestock grazing
- Residential and industrial development
The imported sources are also vulnerable to:
- Wastewater treatment plant discharges
- Seawater intrusion
- Wildland fires in open space areas
In addition, local sources are vulnerable to potential contamination from:
- Commercial stables
- Historic mining practices
No contaminant associated with any of these activities has been detected in SCVWD or Los Altos treated water. The water treatment plants provide multiple barriers for physical removal and disinfection of contaminants. For additional information, visit the SCVWD web site at www.valleywater.org.
We encourage customers to join us in our efforts to prevent water pollution and protect our most precious natural resource.
The Water Quality Lab
Water professionals collect samples from throughout the water system for testing at our state-of-the-art water quality laboratory, which is certified through the stringent Environmental Laboratory Accreditation Program (ELAP). Scientists, chemists, and microbiologists test the water for 318 constituents with equipment so sensitive it can detect levels as low as one part per trillion. In order to maintain the ELAP certification, all of our scientists must pass blind-study proficiency tests each year for every water quality test performed. Water quality test results are entered into our Laboratory Information Management System (LIMS), a sophisticated software program that enables us to react quickly to changes in water quality and analyze water quality trends in order to plan effectively for future needs.
All drinking water, including bottled water, may reasonably be expected to contain at least small amounts of some contaminants. The presence of contaminants does not necessarily indicate that water poses a health risk.
More information about contaminants and potential health effects can be obtained by calling the United States Environmental Protection Agency (EPA) Safe Drinking Water Hotline at (800) 426-4791
The sources of drinking water (both tap and bottled) include rivers, lakes, streams, ponds, reservoirs, springs, and wells. As water travels over the surface of the land or through the ground, it dissolves naturally occurring minerals and, in some cases, radioactive material, and can pick up substances resulting from the presence of animals or human activity.
Contaminants that may be present in source water include:
- Microbial contaminants, such as viruses and bacteria, which may come from sewage treatment plants, septic systems, agricultural livestock operations, and wildlife.
- Inorganic contaminants, such as salts and metals, which can be naturally occurring or result from urban stormwater runoff, industrial or domestic wastewater discharges, oil and gas production, mining, or farming.
- Pesticides and herbicides, which may come from a variety of sources such as agriculture, urban stormwater runoff, and residential uses.
- Organic chemical contaminants, including synthetic and volatile organic chemicals, which are byproducts of industrial processes and petroleum production, and can also come from gas stations, urban stormwater runoff, agricultural application, and septic systems.
- Radioactive contaminants, which can be naturally occurring or the result of oil and gas production and mining activities.
In order to ensure that tap water is safe to drink, the EPA and DDW prescribe regulations that limit the amount of certain contaminants in water provided by public water systems. FDA regulations establish limits for contaminants in bottled water, which must provide the same protection for public health.
Some people may be more vulnerable to contaminants in drinking water than the general population. Immunocompromised people, such as those with cancer undergoing chemotherapy, those who have undergone organ transplants, and those with HIV/AIDS or other immune system disorders; some elderly people; and infants can be particularly at risk from infections. These people should seek advice from their health care providers about drinking water. EPA and Centers for Disease Control and Prevention (CDC) guidelines on appropriate means to lessen the risk of infection by cryptosporidium and other microbial contaminants are available from the Safe Drinking Water Hotline.
As the issue of lead in water continues to be top of mind for many Americans, Cal Water wants to assure you about the quality of your water. We are compliant with health and safety codes mandating use of lead-free materials in water system replacements, repairs, and new installations. We have no known lead service lines in our systems. We test and treat (if necessary) water sources to ensure that the water delivered to customer meters meets all water quality standards and is not corrosive toward plumbing materials.
The water we deliver to your home meets lead standards, but what about your home's plumbing? In California, lead in drinking water comes primarily from materials and components used for in-home plumbing (for example, lead solder used to join copper plumbing, and brass and other lead-containing fixtures).
The lead and copper rule requires us to test water inside a representative number of homes that have plumbing most likely to contain lead and/or lead solder to determine the presence of lead and copper or an action level exceedance (AL). An action level is the concentration of a contaminant which, when exceeded, triggers corrective actions before it becomes a health concern. If action levels are exceeded, either at a customer's home or system-wide, we work with the customer to investigate the issue and/or implement corrosion control treatment to reduce lead levels.
If present, elevated levels of lead can cause serious health problems, especially for pregnant women and young children. Lead in drinking water is primarily from materials and components associated with service lines and home plumbing. Cal Water is responsible for providing high-quality drinking water to our customers' meters, but cannot control the variety of materials used in plumbing components. When your water has been sitting for several hours, you can minimize the potential for lead exposure by flushing your tap for 30 seconds to 2 minutes before using water for drinking or cooking.
If you are concerned about lead in your water, you may wish to have your water tested by a lab. More information about lead in drinking water can be found on the Safe Drinking Water Hotline or at www.epa.gov/safewater/lead.
Results of our lead monitoring program, conducted in accordance with the Lead and Copper Rule, can be found in the 2018 Water Quality Table later in this document. In your system, results from our lead monitoring program, conducted in accordance with the Lead and Copper Rule, were below the action level for the presence of lead.
Testing for Lead in Schools
The State of California now requires that all public schools built before 2010 test for lead in their drinking water by July 1, 2019. We are committed to supporting our school districts' efforts to protect students and ensure that the drinking water at their school sites are below lead limits. We have been working with school districts serving kindergarten through 12th grade to develop sampling plans, test samples, and conduct follow-up monitoring for corrective actions. We have published a summary of local school lead testing from the last year in this year's Water Quality report. For more information, please see our Testing for Lead in Schools web page.
Maximum Contaminant Level (MCL): The highest level of a contaminant that is allowed in drinking water. Primary MCLs protect public health and are set as close to the PHGs (or MCLGs) as are economically and technologically feasible. Secondary MCLs (SMCLs) relate to the odor, taste, and appearance of drinking water.
In Compliance: Does not exceed any applicable primary MCL, secondary MCL, or action level, as determined by DDW. For some compounds, compliance is determined by averaging the results for one source over a one-year period.
Regulatory Action Level (AL): The concentration of a contaminant which, if exceeded, triggers treatment or other required action by the water provider.
Maximum Contaminant Level Goal (MCLG): The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs are set by the EPA.
Maximum Residual Disinfectant Level (MRDL): The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.
Maximum Residual Disinfectant Level Goal (MRDLG): The level of a drinking water disinfectant below which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of disinfectants to control microbial contaminants.
Notification Level (NL): A health-based advisory level for an unregulated contaminant in drinking water. It is used by DDW to provide guidance to drinking water systems.
Primary Drinking Water Standard (PDWS): MCLs and MRDLs for contaminants that affect health, along with their monitoring, reporting, and water treatment requirements.
Public Health Goal (PHG): The level of a contaminant in drinking water below which there is no known or expected risk to health. PHGs are set by the California Environmental Protection Agency's Office of Environmental Health Hazard Assessment without regard to cost or available detection and treatment technologies.
Treatment Technique (TT): A required process intended to reduce the level of a contaminant in drinking water.
Cal Water tests your water for more than 140 regulated contaminants and dozens of unregulated contaminants. This table lists only those contaminants that were detected.
In the table, water quality test results are divided into several major sections (as needed): "Primary Drinking Water Standards," "Secondary Drinking Water Standards," "State-Regulated Contaminants with Notification Levels," and "Unregulated Compounds." Primary standards protect public health by limiting the levels of certain constituents in drinking water. Secondary standards are set for substances that don't impact health but could affect the water's taste, odor, or appearance. Some unregulated substances (hardness and sodium, for example) are included for your information. The State allows us to monitor for some contaminants less than once per year because the concentrations of these contaminants do not change frequently. Some of our data, though representative, are more than one year old.
A list of codes found in the "Source" column and their definitions can be found at the bottom of this page.
Water Quality Table
Primary Drinking Water Standards
|Microbiological||Year Tested||Unit||MCL||PHG (MCLG)||In Compliance||Highest Monthly||Highest Monthly||Source|
(systems with >40 samples/month)
(total coliform rule)
|Radiological||Year Tested||Unit||MCL||PHG (MCLG)||In Compliance||Range||Average||Range||Average||Source|
|Gross alpha particle activity||2010–2018||pCi/L||15||(0)||Yes||ND–10||1.28||n/a||n/a||ER|
|Inorganic Chemicals||Year Tested||Unit||MCL||PHG (MCLG)||In Compliance||Range||Average||Range||Average||Source|
|Nitrate (as nitrogen)||2018||ppm||10||10||Yes||1.51–8.58||5.74||ND–0.7||ND||ER, FR|
|Lead and Copper||Year Tested||Unit||AL||PHG (MCLG)||In Compliance||Distribution System-Wide||Source|
|90th Percentile||Samples > AL|
|Copper||2016||ppm||1.3||0.3||Yes||0.2||0 of 30||IC, ER, WD|
|Lead||2016||ppb||15||0.2||Yes||ND||0 of 30||IC, ER, IM|
|Schools that requested lead sampling in 2018: 16|
|Disinfection Byproducts||Year Tested||Unit||MCL||PHG (MCLG)||In Compliance||Distribution System-Wide||Source|
|Range||Highest Annual Average|
|Disinfectants||Year Tested||Unit||MRDL||MRDLG||In Compliance||Distribution System-Wide||Source|
|Surface Water—Turbidity and TOC||Year Tested||Unit||MCL||PHG (MCLG)||In Compliance||Surface Water Only||Source|
|Highest Level||Lowest Monthly Percent||Highest Level||Lowest Monthly Percent|
|Turbidity (surface water requiring filtration)||2018||NTU||TT||n/a||Yes||n/a||n/a||0.24||0||SO|
|Total organic carbon (TOC)||2018||ppm||TT||n/a||Yes||n/a||n/a||1.9||1.3||VA|
Secondary Drinking Water Standards
|Inorganic Chemicals||Year Tested||Unit||SMCL||PHG (MCLG)||In Compliance||Range||Average||Range||Average||Source|
|Total dissolved solids||2016–2018||ppm||1000||n/a||Yes||370–550||430.63||226–270||258||RL|
|Specific conductance||2016–2018||µS/cm||1600||n/a||Yes||620–910||748.13||340–511||445||SW, IN|
State-Regulated Contaminants with Notification Levels
|Chemical||Year Tested||Unit||NL||PHG (MCLG)||In Compliance||Range||Average||Range||Average||Source|
|Hexavalent chromium||2016–2017||ppb||n/a||n/a||Yes||ND–2.6||1.29||n/a||n/a||ER, EF|
|Inorganic Chemicals||Year Tested||Unit||MCL||PHG (MCLG)||In Compliance||Range||Average||Range||Average||Source|
|Total alkalinity (as CaCO3)||2016–2018||ppm||n/a||n/a||Yes||n/a||n/a||45–88||68||ER|
1 Santa Clara Valley Water District (SCVWD) supply data reported is from 2018. The years prior to 2018 reflect Cal Water data. Water from SCVWD delivered to our system between January and March 2018 may have been from SFPUC via the SFPUC-SCVWD intertie. To see the water quality data during this time period for purchased surface water, go to sfwater.org/index.aspx?page=634.
2 The average nitrate level was 5.74 ppm, with a maximum level of 8.58 ppm. We are closely monitoring the nitrate levels. Nitrate in drinking water at levels above 10 ppm is a health risk for infants of less than six months of age. Such nitrate levels in drinking water can interfere with the capacity of the infant's blood to carry oxygen, resulting in a serious illness; symptoms include shortness of breath and blueness of the skin. Nitrate levels above 10 ppm may also affect the ability of blood to carry oxygen in other individuals, such as pregnant women and those with certain specific enzyme deficiencies. If you are caring for an infant or you are pregnant, you should seek advice from your health care provider.
3 While your drinking water contained varying levels of HAAs it meets the standard. Compliance with the HAA5 MCL is determined by the locational running annual average (LRAA) of samples collected at each sampling location, each quarter of 2018. Some people who drink water containing HAA5 in excess of the MCL over many years may have an increased risk of getting cancer. We are continuously monitoring the levels to ensure we do not exceed the MCL.
4 The turbidity standard for unfiltered supplies is 5 NTU. Turbidity is a measure of the cloudiness of water. We monitor it because it is a good indicator of water quality. High turbidity can hinder the effectiveness of disinfectants.
5 TOC has no health effects; however, TOC provides a medium for the formation of disinfection byproducts. These byproducts include trihalomethanes and haloacetic acids. The treatment technique dictates that a removal ratio of 1 or higher must be achieved. Drinking water containing these byproducts in excess of the MCL may lead to adverse health effects such as liver, kidney, or nervous system problems, and may lead to an increased risk of cancer. Concerns regarding disinfection byproducts are based upon exposure over many years.
6 The previous MCL of 0.010 mg/L (10 ppb) for hexavalent chromium was withdrawn on September 11, 2017, and there is currently no MCL in effect. The state recommends that any hexavalent chromium results above the detection limit of 1 ppb still be reported.
|AS||Internal corrosion of AC water mains|
|BD||Biodegradation byproduct of TCE and PCE groundwater contamination|
|BH||Residue of banned herbicide|
|BI||Residue of banned insecticide|
|BN||Banned nematocide that may still be present in soils due to runoff/leaching from former use on soybeans, cotton, vineyards, tomatoes, and tree fruit|
|BR||Residue of banned insecticide and rodenticide|
|BT||Banned nematocide that may still be present in soils due to runoff and leaching from grain and fruit crops|
|CF||Discharge from industrial chemical factories|
|CP||Discharge from chemical plants and other industrial activities|
|DC||Discharge from industrial and agricultural chemical factories and dry cleaning facilities|
|DI||Byproduct of drinking water disinfection|
|DK||Decay of natural and manmade deposits|
|DS||Drinking water disinfectant added for treatment|
|EF||Discharge from electroplating factories, leather tanneries, wood preservation, chemical synthesis, refractory production, and textile manufacturing facilities|
|EN||Naturally present in the environment|
|ER||Erosion of natural deposits|
|EX||Extraction and degreasing solvent; used in manufacture of pharmaceuticals, stone, clay and glass products; fumigant|
|FD||Discharge from factories, dry cleaners, and auto shops (metal degreaser)|
|FE||Human and animal waste|
|FI||Fire retardants; ceramics; electronics; solder|
|FL||Water additive that promotes strong teeth; discharge from fertilizer and aluminum factories|
|FM||Primary component of some fumigants|
|FR||Runoff and leaching from fertilizer use; leaching from septic tanks and sewage|
|FW||Manufacture of food wrappings|
|GP||Internal corrosion of galvanized pipes; discharge from electroplating and industrial chemical factories and metal refineries; runoff from waste batteries and paint|
|HB||Runoff/leaching from herbicide used on beans, peppers, corn, peanuts, rice, and ornamental grasses|
|HD||Runoff from herbicide use for terrestrial and aquatic weeds; defoliant|
|HP||Breakdown of heptachlor|
|HR||Runoff from herbicide used on row crops|
|HS||Runoff from herbicide used on soybeans, vegetables, and fruits|
|HT||Runoff from herbicide use for terrestrial and aquatic weeds|
|IA||Discharge from industrial and agricultural chemical factories; leaching from hazardous waste sites; used as cleaning and maintenance solvent, paint and varnish remover, and cleaning and degreasing agent; byproduct of production of other compounds and pesticides|
|IC||Internal corrosion of household plumbing systems|
|IF||Discharge from industrial factories; degreasing solvent; propellant and refrigerant|
|IL||Runoff/leaching from insecticide used on cattle, lumber, and gardens|
|IM||Discharge from industrial manufacturers|
|IN||Runoff/leaching from insecticide used on cotton and cattle|
|IO||Substances that form ions when in water|
|IT||Runoff/leaching from insecticide used on field crops, fruits, and ornamentals, especially apples, potatoes, and tomatoes|
|IV||Runoff/leaching from insecticide used on fruits, vegetables, alfalfa, and livestock|
|LA||Runoff from landfills; discharge of waste chemicals|
|LE||Leaking underground storage tanks|
|MA||Discharge from metal refineries and agricultural chemical factories; byproduct of chlorination reactions in wastewater|
|MD||Discharge from metal-degreasing sites and other factories|
|MF||Discharge from metal factories|
|MR||Discharge from metal refineries, coal-burning factories, and electrical, aerospace, and defense industries|
|MS||Discharge from metal degreasing sites and other factories; dry cleaning solvent; refrigerant|
|MU||Municipal and industrial waste discharges|
|OC||Runoff from orchards; glass and electronics production waste|
|OD||Discharges of oil-drilling waste and from metal refineries|
|OM||Naturally occurring organic materials|
|OR||Leaching from ore-processing sites; discharge from electronics, glass, and drug factories|
|PC||Discharge from petroleum and chemical factories|
|PD||Discharge from plastics, dyes, and nylon factories; leaching from gas storage tanks and landfills|
|PG||Discharge from petroleum, glass, and metal refineries; discharge from mines and chemical manufacturers; runoff from livestock lots (feed additive)|
|PH||Inherent characteristic of water|
|PI||Discharge from pharmaceutical and chemical factories; insecticide|
|PR||Inorganic chemical used in solid rocket propellant, fireworks, explosives, flares, matches, and a variety of industries; usually gets into drinking water as a result of environmental contamination from historic aerospace or other industrial operations that used or use, store, or dispose of perchlorate and its salts|
|PT||Discharge from petroleum refineries|
|PV||Leaching from PVC piping; discharge from plastics factories; biodegradation byproduct of TCE and PCE groundwater contamination|
|RB||Discharge from rubber and chemical factories; inert ingredient in pesticides|
|RC||Runoff from herbicide used on row crops, range land, lawns, and aquatic weeds|
|RF||Discharge from refineries and factories; runoff from landfills and cropland|
|RI||Runoff/leaching from rice herbicide|
|RL||Runoff/leaching from natural deposits|
|RP||Discharge from rubber and plastic factories; leaching from landfills|
|RR||Runoff from herbicide used on row crops and along railroad and highway rights-of-way|
|RS||Residue from some surface water treatment processes|
|RT||Runoff/leaching from nematocide used on croplands|
|RW||Runoff from herbicide used on rights-of-way, and crops and landscape maintenance|
|SF||Leaching of soil fumigant used on rice, alfalfa, and grape vineyards|
|SM||Discharge from steel/metal, plastic, and fertilizer factories|
|SP||Discharge from steel and pulp mills and chrome plating|
|TC||Discharge from industrial and agricultural chemical factories; solvent used in production of TCE, pesticides, varnish, and lacquers|
|TX||Discharge from textile-finishing factories|
|UN||Underground gas tank leaks|
|VA||Various natural and manmade sources|
|WD||Leaching from wood preservatives|
|WI||Emissions from waste incineration and other combustion|
|WP||Discharge from wood preserving factories, cotton, and other insecticidal/herbicidal uses|
|WS||Leaching from linings of water storage tanks and distribution mains|
|UR||Unregulated constituents with no source listed and that do not have standardized “source of substance” language|
A full-color, printable version of this report in PDF format is also available.
If you have any questions about your water quality table, please Contact Us.