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Water Supply


AMWC obtains all of its water from two distinct yet interrelated groundwater sources - the Salinas River Underflow and the Atascadero  Groundwater Basin. Water from these sources resides in the tiny spaces between sands and gravels until it is pumped to the surface by AMWC's wells. These sands and gravels act as natural filters, resulting in water that is clean and clear. Shallow wells (70' - 100') pump water from the Salinas River Underflow, while deeper wells (300' - 500') pump from the Atascadero Groundwater Basin. 

Water Quality

Water Quality Report

AMWC consistently produces water that meets or exceeds all state and federal drinking water standards.  Water quality samples are regularly taken at the wells and throughout the entire distribution system.  AMWC monitors these samples for all contaminants as required by the USEPA, the Safe Drinking Water Act, and Primary Drinking Water Standards, and follows all guidelines according to the national primary drinking water regulations.  AMWC is required to keep all water analysis results on file for three years.  A summary of water quality sampling results can be found in the Consumer Confidence Report prepared each year by AMWC. A copy of the report can be downloaded in PDF format (by clicking on the Water Quality Report image to the left) or obtained at the AMWC administrative office at 5005 El Camino Real.

Treatment & Disinfection
The majority of AMWC’s groundwater requires no treatment other than chlorination and the “natural filtration” that occurs when the water passes through sand and gravel formations. Water produced from AMWC’s wells is disinfected with chlorine. We maintain positive chlorine residuals both at our wells and throughout the distribution system in order to maintain disinfection levels. We pay particular attention to circulation in our reservoirs to maintain proper chlorine levels there as well.

Pink residue is generally not a problem with water quality. In fact, pink residue is likely a result of airborne bacteria, which produce a pinkish or dark gray film on regularly moist surfaces. Such surfaces include toilet bowls, showerheads, sink drains, and tiles.

Some people have also noted that the pink residue appears in their pet's water bowl, which causes no apparent harm to the pet and is easily cleaned off.

Many experts agree that the bacteria that causes these pink stains is most likely Serratia marcesens, a bacteria which is found naturally in soil, food, and in animals. Serratia, which produce a characteristic red pigment, thrive on moisture, dust, and phosphates and need almost nothing to survive. The pinkish film often appears during or after construction or remodeling, when dust and dirt containing Serratia bacteria are stirred up. Once the bacteria is airborne, it will seek a moist location in which it can grow. Some people have reported that the pink residue only appears during certain times of the year, when their windows are left open for most of the day. This bacteria is present in a number of environments and wind can carry the airborne bacteria or stir up dust in which the bacteria is present. The use of activated carbon filters, which remove chlorine from the water, can make the problem worse. The absence of the normal levels of chlorine in tap water allows Serratia to thrive.

How do I get rid of pink residue?
The best solution to this problem is to continually clean the involved surfaces to keep them free from bacteria. Compounds containing chlorine work best, but keep in mind that abrasive cleaners may scratch fixtures, making them more susceptible to bacterial growth. Chlorine bleach can be used periodically to disinfect the toilet and help to eliminate the occurrence of the pink residue. An easy way to do this is to stir three to five tablespoons of fresh bleach to the toilet tank, flush the toilet to allow the bowl to be disinfected, and add another dose of bleach to the tank as it is refilling. The use of toilet "cakes" containing disinfectant can help keep the problem under control. By keeping bathtubs and sinks wiped down and dry, the formation of pink residue can be avoided.

Hard Water
The high calcium and magnesium levels found in the geologic formation (aquifer) from which AMWC produces its water causes "hardness." While such minerals offer positive health benefits, the hardness can stain fixtures and require greater amounts of detergents than soft water. While hardness can be reduced by the use of water softeners, the brine discharge from the softeners eventually ends up in the groundwater, further increasing its hardness.

Periodically, AMWC receives comments from customers about odors that they detect in the water. The chlorine used for disinfection of the water can sometimes cause an odor. Other times an odor may be the result of low levels of hydrogen sulfide in the water that can impart a sulfur smell. Hydrogen sulfide, in the minute amounts found in the water produced from AMWC wells, is harmless. Normally, customers notice the sulfur odor during periods of peak demand, which is typically summer and early fall when water levels in the wells are lowest. Customers can often reduce odors through the use of household reverse osmosis and carbon filters. Sometimes in-home treatment devices, such as water filters and softeners that are not maintained on a regular basis, can impart an odor into the customer’s tap water. If you have concerns over an odor in your water, please contact AMWC at 466-2428.

Source Water Protection
Activities in and around the wells that produce our water can directly impact its quality. For this reason, AMWC monitors activities that take place in areas that drain toward our wells (i.e., the “watershed”) and conducts daily inspections of the immediate vicinity of each well to identify and eliminate potential sources of contamination or vandalism. Community and private sewer systems, animal waste, leaking underground fuel tanks, industrial discharges, agricultural activities, pesticide/herbicide use, and storm water runoff are possible sources of contaminants to the water supply. However, no contaminant associated with these activities has been detected in the water produced from AMWC’s wells.

Girl Drinking Water

Maintaining or Restoring Water Quality in Buildings With Low or No Use
EPA recommends that building owners and managers take proactive steps to protect public health by minimizing water stagnation during closures and taking action to  address building water quality prior to opening.  

Click HERE to read the complete EPA recommendations. [PDF Format]

Water Quality
Private Wells

Private Wells


In 1913, AMWC was deeded all water rights within its service area to hold in trust for its shareholders. As trustee, AMWC has the authority and responsibility to manage these groundwater resources. AMWC has a policy that restricts the drilling and use of private wells within its service area. AMWC's intent is to protect the groundwater resources of the shareholders and provide for the equitable distribution of these resources. AMWC allows the drilling and use of some private wells in those areas where the wells are not likely to have significant impacts on the groundwater resources of AMWC. AMWC prohibits the drilling and use of new wells in areas that overlie the Atascadero Sub-basin, the alluvial deposits of the Salinas River, or other areas that could significantly impact the quantity, quality, or recharge of groundwater.

Refer to Board Policy

Nacimiento Water Project

Nacimiento Water Project


The Nacimiento Water Project (NWP) regional raw water transmission facility delivers water from Lake Nacimiento to communities in San Luis Obispo County. The NWP includes 45 miles of pipeline ranging from 12 inches to 36 inches in diameter, an intake structure at Nacimiento Lake, three pump stations ranging from 1,200 horsepower (hp) to 3,500 hp, and three water storage tanks ranging from 300,000 gallons to 850,000 gallons. The NWP is designed to deliver 15,750 acre-feet of water per year (AFY). Atascadero Mutual Water Company (AMWC) has contracted for 2,000 AFY, which will significantly improve its ability to meet the current and future water needs of its shareholders. One acre-foot of water is approximately 326,000 gallons. The County of San Luis Obispo was the lead agency for the $176.1 million NWP. In 2004, AMWC entered into a Delivery Entitlement Contract with the County for participation in the project, with AMWC’s share of the project costs being approximately $39 million to be paid over 30 years. Other agencies currently participating in the project are the City of Paso Robles, Templeton Community Services District, and the City of San Luis Obispo. The project has already had a large effect on connection fees and water rates paid by AMWC’s shareholders. Construction on the project is complete, and AMWC began taking deliveries of water in the summer of 2012.

The NWP is owned, managed, and operated by San Luis Obispo Flood Control and Water Conservation District. For more information, visit 

Urban Water Management

Urban Water Management Plan

A Conservation Plan for Our Finite Water Resources

AMWC looks ahead to efficiently plan for your future water supply. The 2015 Urban Water Management Plan (draft) provides an overview of water supply sources, conservation measures, programs, and incentives to ensure the wise and beneficial use of your water resources.

For further questions about the plan, which is updated every five years as part of the California Water Code, please contact

2020 Urban Water Management Plan [pdf]

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