Water Submetering for Mobilehome and RV Parks

Why Parks Are Their Own Case

Most California writing on water submetering is about apartments and SB 7. A mobilehome park is a different animal. Residents usually own their homes and rent the space underneath them. The water runs through a network of park-owned mains and laterals that the park, not the water purveyor, is responsible for. And the law that governs the resident relationship is the Mobilehome Residency Law (MRL), Civil Code §798 and following, which carries its own water-billing rules.

SB 7's definitions are built around a "landlord" renting a "dwelling unit" in a property served by a single master meter. It does not mention mobilehome parks. The MRL, meanwhile, has a parallel rule in §798.40(c) that borrows SB 7's billing structure and applies it to spaces. The sound reading, and the one this guide follows, is that a park billing its residents for water is governed by the MRL. If you also own apartments, our guide to Water Submetering for Apartment Communities covers the SB 7 side, and California SB-7 & Submetering Compliance gives the broader picture.

The Right to Bill Water Separately: §798.41

Civil Code §798.41 is where separate billing starts. Unless the rental agreement says otherwise, management may bill residents for utility service, water and sewer included, separately from rent. Three conditions come with that right:

• Rent comes down first. At the first separate billing, the space rent must drop by that space's average cost for the utility over the prior 12 months.
• Charges are itemized. The resident has to be able to see what the water charge is and how it was arrived at.
• Older agreements wait for renewal. For rental agreements entered into before 1991, the section applies only once the agreement is extended or renewed.

So the conversion needs a paper trail before the first bill: twelve months of master-meter bills, a per-space average, and a matching rent adjustment for every space.

How Charges Are Calculated: §798.40(c)

Section 798.40(c) was added by AB 1061 in 2021, and AB 604, effective January 1, 2024, made clear that it applies "including where the water purveyor or the mobilehome park is subject to the jurisdiction" of the Public Utilities Commission. It applies SB 7's billing structure to parks. "Water service" here includes water, sewer, stormwater and flood control charges, so sewer is billed under the same rules as water.

The formula is also the ceiling. Section 798.40(c) provides for no markup: the one addition to the purveyor's own charges is the capped admin fee. Separately, §798.40(e) preserves management's ability to recover the costs of its internal water system where the rental agreement or local rules allow it. That is a question for your agreements and any local rent ordinance, not something to fold into the monthly water bill.

Late fees: the park rule is not SB 7

SB 7 sets detailed late-fee caps for apartments. Section 798.40 does not: it contains no late-fee cap, no pre-lease disclosure list and no leak-credit rule. That is a gap, not a licence. Whether and how much you may charge for a late water payment depends on your rental agreements and the rest of the law that governs your park, so settle it with counsel before a late fee ever appears on a water bill. Until then, leaving late fees off the water bill is the safe default.

What Every Bill Must Show: §798.40(a)–(b)

The MRL's billing requirements are short, but they are not optional. For each billing period, the bill must:

• State the charges for the period.
• Show the opening and closing meter reads for the space.
• Name the billing agent, if a third party prepares or collects the bills.

Separately, management must post the serving utility's residential rate schedule, or the web address where it can be found, and give a resident a free copy on request.

Those are the minimums. A bill that also shows consumption, the method used for each line and the admin fee as its own line answers most questions before they are asked.

Summary only. The statutes carry conditions this table leaves out.

Where the Public Utilities Code Fits

A park that resells water could, in principle, look like a water utility. Two sections of the Public Utilities Code say when it isn't.

Parks served by a water corporation: PUC §2705.5

A mobilehome park with a water submeter system "is not a public utility" if each user is charged the rate that would apply if the user were receiving water directly from the water corporation, or if management complies with Civil Code §798.40(c). That second branch matters. Before AB 604, the "same rate as the utility" language sat awkwardly next to an admin fee. The amendment tied the two together for parks, so a park billing under §798.40(c), fee included, keeps its non-utility status. The same tension remains unresolved for apartments.

One point of confusion is worth clearing up. Section 2705.5 mandates no credits or discounts for water. The "master-meter discount" that park owners hear about comes from PUC §739.5, which governs electricity and gas. There is no water equivalent. Tariffs can also carry their own conditions: Golden State Water's Rule 19, for example, allows submetering for a mobilehome park at the rate the utility would otherwise charge, and prohibits other resale without the utility's special agreement. Read your purveyor's rules as well as the statute.

Parks with their own supply: PUC §2705.6

A park that supplies water from its own sources, such as a well, is not a water corporation. But there is a safeguard. If tenants holding at least 10% of the connections complain within 12 months, the CPUC can rule on the park's rates and order refunds, and the park must give residents written notice of that right. If your park runs its own supply, make sure that notice has gone out.

Los Angeles: LADWP Rule 18

LADWP is a municipal utility, and its Rule 18 covers water as well as electricity. It prohibits resale, but allows residential units, mobilehome parks and commercial units to be submetered and billed at "no more than if the Department provided the water" directly. Separate bills showing the reads and posted rates match what §798.40 already requires. It then goes further than state law in two ways:

• No fees of any kind. "No additional costs, fees, service charges… of any nature," including meter-reading, account and equipment charges.
• Actual use only. Any allocation must charge each user for "the amount actually used."

That puts Rule 18 in direct tension with the §798.40(c) admin fee. AB 604 settled the fee question for parks under CPUC jurisdiction, but LADWP is not a CPUC utility, and no statute or ruling we know of resolves which rule wins in Los Angeles. Until that changes, do not build a Los Angeles park's water program on the assumption that the admin fee is recoverable.

Meters: Type Approval, Accuracy and the County Sealer

A water meter whose reading sets a resident's charge is a commercial device under California's weights-and-measures law. Business and Professions Code §12500(e) defines "commercial purposes" to include a measurement on which a charge for service is based, and §12500.5 makes it unlawful to use such a device unless its type has been approved. Section 12240(g) names mobilehome parks and RV parks specifically among the sites that pay county device fees for water submeters.

• ±1.5%: the acceptance and maintenance tolerance for accuracy class 1.5 under NIST Handbook 44 §3.36.
• $6: the maximum county device fee per water submeter per space (BPC §12240(g)(1)(A)).
• $0.50: the state's annual administrative fee per domestic water submeter, on top of the county fee (4 CCR §4075).

California previously had its own modification to the national water-meter code. That modification (4 CCR §4002.6) has been repealed, so NIST Handbook 44 §3.36 applies as published. For accuracy class 1.5, the tolerance is ±1.5% at acceptance and in maintenance. At minimum flow, the limits are 1.5% over- and 5.0% under-registration for meters other than multi-jet, and 3.0% either way for multi-jet meters. Handbook 44's user requirements (UR.2) also address access to the customer indication, including a clear standing space of 30 × 36 × 78 inches. Plan meter locations with that in mind.

Two practical points on the rules around the meter:

• Inspection interval. 4 CCR §4070 lists "Water Submeter (Domestic Service)" at 10 years and "Water Submeter (All Others)" as annual. The regulation doesn't define domestic service, so confirm with your county sealer which row it applies to your meters, and to any meter serving a non-residential building in the park.
• The fee statute has a sunset. BPC §12240, as amended by AB 1304 (2023), is set to sunset on January 1, 2029. Check the current version before budgeting past that date.

AWWA product standards (C700, C710, C712, C713, C715) are industry standards, not California's legal test. Type approval and Handbook 44 are.

RV Parks

RV parks sit under a different statute, the Recreational Vehicle Park Occupancy Law (Civil Code §799.20 and following), and it says nothing about water billing or submeters. What it does require:

• Disclose fees up front. The registration agreement must state the rent and "the fees, if any, to be charged for services" (§799.43). If you bill water, say so there, and say how.
• Unpaid utilities have consequences. Unpaid "utilities" are grounds for a three-day notice (§799.65).

Three more points shape an RV park's water program:

• The meters are still regulated. BPC §12240(g) names RV parks, so type approval and the county device fee apply to RV-park water submeters just as they do in a mobilehome park.
• PUC §2705.5 names "mobilehome park or a multiple unit residential complex." It does not name RV parks, and whether it reaches them is unsettled. Don't assume the non-utility safe harbor extends to your RV park.
• A sensible default. With no statute setting the method, billing measured use at the purveyor's rates, keeping common-area water off the bill and showing the reads on every bill is the easiest program to defend. In LADWP territory, check Rule 18 before charging any fee.

Practical Guidance for a Park Retrofit

Meter placement at each space

Put each meter on the lateral that feeds one space and nothing else, past the last branch to any shared fixture. A meter that also sees a shared hose bib or a neighboring space is exactly the problem §798.43 describes. Place it where the reader can get to it without entering the home or the resident's enclosed yard, where it is protected from vehicles and frost, and with a shutoff valve on the park side so it can be serviced without interrupting the whole loop. Record every meter's serial number against its space number before the first read, and keep that map current.

Reading

Read every space on the same schedule, as close as possible to the date the master meter is read, so each period's space totals line up with the bill you are passing through. Whatever the method, keep the raw reads. A resident who disputes a bill should be able to see the same numbers you billed from.

Leak detection on park-owned lines

Park mains and laterals are often older than anything else on the property, and they leak underground where nobody sees it. Submetering gives you a tool for finding it. Every cycle, compare the master meter with the sum of the space meters plus any metered common areas. The gap is water no space meter recorded: common-area use, meter error, and losses from park-owned pipe. Because common-area water can't be billed to residents, that gap is the park's cost either way. Track it over time. A gap that grows, or water still flowing through the master meter overnight when every space meter is idle, points to a leak worth chasing.

Frequently Asked Questions

Checklist: Before the First Water Bill

Sources

Accessed September 2026.

• California Civil Code §798.40 — bill contents, rate posting and the water-billing structure for parks
• California Civil Code §798.41 — separate utility billing and the rent reduction
• California Civil Code §798.43 — common-area use on a resident's meter
• California Civil Code §798.3 — RVs treated as mobilehomes after nine months
• California Civil Code §799.43 and §799.65 — RV park registration agreements and unpaid utilities
• California Civil Code §1954.205 (part of §1954.201–.219, SB 7) — the apartment rules used for comparison
• California Public Utilities Code §2705.5 and §2705.6 — when a park is not a water utility
• California Business and Professions Code §12240, §12500 and §12500.5 — device fees, commercial purposes and type approval
• California Code of Regulations, Title 4, §4070 and §4075 — inspection intervals and state fees; NIST Handbook 44 §3.36 via the CDFA 2024 Field Reference Manual
• CPUC, Mobilehome Park Utility Upgrade Program update (February 24, 2026) — D.20-04-004, electric and gas only
• Golden State Water Company Rule 19; LADWP Rule 18 — utility rules on resale and submetering