To protect the community of Mammoth Lakes’ water supply, the Mammoth Community Water District (MCWD) has a cross-connection control and backflow prevention program in place. The program requires backflow prevention assemblies to be installed and annually tested where cross-connection can occur. The program is mandated by multiple authorities.

What is a backflow prevention assembly?

Backflow prevention assemblies are devices designed to prevent water from flowing back into the public water delivery system.

Why do I have to install a backflow prevention assembly?

To protect customers receiving water from the Mammoth Community Water District from potential water contamination.

When is a backflow prevention assembly required?

Any location where there is actual or potential uncontrolled cross-connections. Common examples of potential cross-connections locations include:

  •      Irrigation systems (residential, commercial and public)
  •      Fire Sprinkler Systems
  •      Swimming pools and spas
  •      Hydronic systems (common example in Mammoth: radiant heating)
  •      Hose Bibs

Other cities do not require backflow prevention assemblies or annual testing for lawn irrigation systems, why does MCWD?

Due to our mountainous environment (large elevation changes) we have increased chances of backpressure. Furthermore, our water supply is limited to our basin and cannot be imported. MCWD follows the recommendations from the State of California Health and Safety Code. Lawn irrigation systems are considered a high-risk for cross contamination because a backflow incident could introduce fertilizers, pesticides and other lawn chemicals (as well as insects and animal waste) into the community’s drinking water, which could be lethally hazardous.

If I do not use my irrigation system, do I still have to have my device tested?

MCWD will grant a one year waiver from the testing requirement if the property owner decides not to utilize their irrigation system. If the property owner decides to discontinue use of their irrigation system, they must remove the assembly, cut and cap the irrigation system to be removed from the requirement going forward. An inspection of the removed and capped system is required.

Do backflow prevention assemblies need to be tested?

Yes, backflow prevention assembly testing is required, at minimum, on an annual basis by a certified tester. A list of certified testers can be found below. The average cost is $75.

Who are the mandating authorities regarding cross-connection control and backflow prevention?

Code of Federal Regulations, Safe Water Drinking Water Act of 1986
Code of California Regulations Title 17 and Title 22
State of California Health and Safety Code Section 13114.7
California Plumbing Code
California Fire Code
Mammoth Community Water District Water Code, Chapter 12, Division 3, Section 3.34


Cross-Connection Control Specialist
Marc Hannon
760-934-2596 x 295
Click here to email Marc Hannon

Backflow Test Report Form:

Backflow Prevention Assembly Test Report – Blank

Certified Approved Testers:

Tester # Name Company Expiration Phone
11259 Erik Westfall A & D Plumbing 08/31/24 760-937-0805
06331 Manny Bravo Bravo Gardens 06/30/25 818-519-0009
13119 Phil Watts Phil Watts Landscape 11/30/25 760-937-3589
16389 James Gray Grasshopper Inc. 03/31/23 760-382-1975
17268 Jason Volentine JB Fire Systems 05/31/25 775-843-3558
06541 Tom Sandlin The Plumbing Co. 02/28/23 760-379-0799
18046 Tarek Nuttal Highland Plumbing 12/31/23 760-914-9184
18070 Howard Spezzia A Reliable Plumber 12/21/23 626-252-5836
18500 Matt Graef Matt Graef 12/31/2024 760-914-7108