Backflow Prevention in Marin County - MMWD
Backflow Prevention Marin County (MMWD Compliance)
If you received a Marin Municipal Water District (MMWD) letter requiring a backflow prevention assembly, you’re not alone, MMWD is issuing notices to residential and commercial properties across Marin County as part of its cross-connection control program.
Local Plumbing helps Marin homeowners, HOAs, and businesses install MMWD-approved reduced pressure backflow preventers (RP) at the water meter (or designated hazard point) so you can meet your deadline, pass testing, and stay compliant.
Call now to schedule a site visit and we’ll confirm your meter layout, required RP size, install location, and what’s needed for test access and annual compliance.
What the MMWD Backflow Letter Means
MMWD’s notice is typically triggered after a cross-connection survey identifies a potential backflow hazard. The letter commonly requires:
- Installation of an approved reduced pressure backflow preventer (RP / RPZ)
- Installation at the water meter (or at the specified hazard connection point)
- Testing immediately after installation by a certified tester recognized by MMWD
- Annual testing thereafter, submitted through MMWD’s reporting system
- Completion by the due date on your notice
If you’re a property owner, property manager, or business in Marin County, this is one of those items where doing it “almost right” can still fail inspection/testing - layout and accessibility matter.
What Is a Backflow Preventer (And Why MMWD Requires It)?
Backflow is when water flows the wrong direction—potentially pulling contaminants into the public drinking water system due to back-siphonage or backpressure. Certain property conditions increase risk, including (examples):
- Irrigation systems / landscape watering
- Commercial equipment, process piping, or chemical dispensing
- Boilers, hydronic systems, or make-up water connections
- Fire sprinkler connections (depending on configuration and authority requirements)
- Pools/spas, hose bibb exposures, or auxiliary water sources
An RP backflow preventer is commonly required when the hazard level is higher because it provides stronger protection than simpler devices.
MMWD Standard Installation Requirements (What We Build To)
MMWD provides a standard installation diagram and notes that typically require:
1) Approved assembly only
- The backflow assembly must be MMWD-approved (specific makes/models are listed by the District).
2) Install at the meter with proper orientation and clearance
- Installed on the customer’s property, commonly at the meter
- Maintain clearance around the assembly for testing and maintenance (often 12 inches around)
3) No extra connections between the meter and the backflow
MMWD’s standard notes generally prohibit:
- No outlets, tees, taps, bypasses, unions, or other connections between the water meter and the backflow prevention assembly
- Strainers / PRVs and other appurtenances are typically placed after the assembly unless the District specifically allows otherwise
4) Proper height & protection
- Installed above grade for access (many standards show roughly 12" min to 30" max above finished grade)
- Protected from vehicle impact and freeze damage where applicable
5) Closed system considerations (thermal expansion)
An RP assembly can create a
closed water system—which often means your building may need
thermal expansion protection (we’ll evaluate this during the install plan).
Our Backflow Process (Fast + Compliant)
Step 1: Site check at the meter
We verify:
- Meter configuration & property line layout
- Required device type (RP) and estimated sizing
- Space for 12” clearance and tester access
- Whether a PRV location is required and where it can go without violating the “no connections before backflow” rule
Step 2: Install the MMWD-approved RP assembly
We build the assembly so it’s:
- Clean, serviceable, and testable
- Correct elevation above grade
- Ready for immediate testing
Step 3: Testing + submittal
MMWD requires certified testing and online submission. We can:
- Coordinate testing with a recognized tester, or
- Provide testing if available for your project’s requirements and schedule
Step 4: Annual compliance planning
We’ll help you set up a simple annual reminder plan so you don’t get caught with a missed test.
Cost Factors (What Affects Backflow Installation Pricing in Marin)
Backflow installs vary widely depending on the meter area and required protection. Pricing is commonly affected by:
- RP size and approved model availability
- Concrete/asphalt cutting and restoration at the meter box
- Need for bollards/guard posts for vehicle protection
- Depth of service line and re-piping complexity
- Whether a pressure regulator must be relocated/installed
- Testing coordination and access limitations
If you want, we can provide good/better/best options (basic compliance vs. upgraded protection and cleaner layout).
Backflow Prevention FAQs (MMWD / Marin County)
“Can I install it anywhere I want?”
Usually no. MMWD letters often specify at the meter or at the hazard point. The District also has layout rules to keep it serviceable and testable.
“Do I really need annual testing?”
Yes—MMWD typically requires immediate post-install testing and annual testing thereafter.
“Will this affect my water pressure?”
It can, depending on existing pressure, piping, and whether you already have a PRV. We’ll review options to keep performance strong while staying compliant.
“Why is my neighbor getting a letter too?”
MMWD is surveying and enforcing cross-connection control more consistently across Marin County—especially where property uses or plumbing conditions increase risk.
Schedule Your Backflow Install
If your notice has an install-by deadline, don’t wait—equipment availability, concrete work, and testing schedules can tighten fast.
Local Plumbing will:
- Confirm exactly what MMWD is asking for
- Install the correct MMWD-approved RP backflow preventer
- Ensure the assembly is test-ready and laid out to meet MMWD’s standard diagram requirements
- Coordinate the certified test and submission
Call Local Plumbing or request an estimate online to get your backflow project on the calendar.
Central & South Marin
- San Rafael backflow prevention
- Corte Madera backflow preventer installation
- Larkspur backflow testing & installation
- Kentfield RP backflow preventer
- Greenbrae backflow compliance
- Ross backflow prevention assembly
- San Anselmo backflow install
- Fairfax backflow preventer
- Mill Valley backflow prevention (RP / RPZ)
- Sausalito backflow preventer at meter
- Tiburon backflow prevention assembly
- Belvedere backflow preventer installation
- Strawberry backflow compliance
- Marin City backflow prevention
North Marin
- Novato backflow prevention
- Nicasio backflow assembly installation
West Marin / Coastal Marin
- Point Reyes Station backflow prevention
- Inverness backflow assembly
- Olema backflow compliance
- Stinson Beach backflow preventer
- Bolinas backflow prevention
- Muir Beach backflow assembly
- Dillon Beach backflow prevention
- Tomales backflow preventer
- Marshall backflow prevention
- Woodacre backflow compliance
- Lagunitas / Forest Knolls backflow prevention
