Private Water in MHPs: Underwriting the PFAS and Lead Pipe Rules

Published September 27, 2026

Nearly 70% of mobile home parks that run their own water systems violated federal safe drinking water rules over a five-year period, according to an Associated Press analysis of EPA data published in July 2025. More than half failed to perform or properly report at least one required test. That is the compliance baseline that two federal rules now land on: a 4.0 parts-per-trillion limit on two PFAS chemicals, with initial monitoring due by April 26, 2027, and a lead pipe rule whose compliance date is November 1, 2027.

For a buyer, the point is not the headline. It is that a mobile home park (MHP) with a private well is, in regulatory terms, a small water utility — and a small utility can carry a capital and operating tail that the seller's T-12 has never had to show.

What we know about the rules reaching a mobile home park water system

This section sticks to what EPA, the Federal Register, and named summaries of the rules state.

• Who is covered. Under the Safe Drinking Water Act, a system serving at least 15 connections or regularly serving at least 25 people for 60 or more days a year is generally a public water system, per EPA. A park serving year-round residents typically counts as a community water system — the category both rules below reach.
• PFAS limits. EPA's April 2024 rule set enforceable limits of 4.0 parts per trillion each for PFOA and PFOS, two per- and polyfluoroalkyl substances (PFAS). Per the Federal Register notice of May 20, 2026, EPA has proposed keeping those limits but letting systems request a two-year exemption that moves the compliance date from April 26, 2029 to April 26, 2031. The extension would not be automatic: per EPA, a system has to apply for it, and in states without primacy for these limits EPA would grant it directly. Monitoring and reporting would still follow the 2024 rule's timeframes, so the initial monitoring deadline of April 26, 2027 is not moved by that proposal.
• Other PFAS. A separate May 2026 EPA proposal would rescind the 2024 limits for PFHxS, PFNA, GenX chemicals, and the hazard index mixture. Per EPA, the comment period on both proposals closed July 20, 2026; neither was final at the time of writing.
• Small-system economics. The extension proposal notes that point-of-use treatment could offer small systems annual savings of roughly 40% to 72% versus centralized treatment, and that fewer than half of systems in an American Water Works Association (AWWA) 2025 survey were confident they could fund compliance through rates and fees.
• Lead pipes. EPA's Lead and Copper Rule Improvements (LCRI), finalized in October 2024, carry a compliance date of November 1, 2027, per the National League of Cities' summary of the rule. They lower the lead action level from 15 to 10 micrograms per liter and require replacement of lead and certain galvanized service lines under the system's control at an average of roughly 10% a year, targeting completion by 2037. Systems serving 3,300 or fewer people receive some flexibilities.

Two cautions sit on top of that list. Rules under proposal may change before they are final, and states with primacy can be stricter than the federal floor — verify current requirements with the state drinking water program before relying on any date above.

What this could mean for a park that runs its own water

What follows is a read of the data, not a prediction of how any specific park will test.

The first implication is timing. A park acquired this fall that operates its own community water system may produce its first PFAS results inside the first hold year. Whatever the compliance date for treatment ends up being, a result above 4.0 parts per trillion would likely become a known liability the moment it is reported — to residents through required notices, to a lender at refinance, and to the next buyer at exit. The 2031 extension, if finalized, may buy time to fund a fix, but only for a system whose owner requests it, which makes whether the seller has applied, or intends to, a live diligence question. Either way, it does not appear to delay the discovery.

The second is who controls the pipes. On a municipal system, the lead service line up to the property is typically the city's problem. In a park that runs its own system, the mains, the service lines, and often the connection to each home belong to the owner. The LCRI's replacement obligation attaches to lines under the system's control, which in a private-water park may be most of them. Parks built before the federal lead ban in the mid-1980s, or with undocumented galvanized lines, tend to be where the inventory question matters most.

The third is the compliance record itself. Given the AP's finding that monitoring and reporting failures were common, a park's history in its state's drinking water database may say as much about the operator as its rent roll. A history of missed samples is not a contamination finding, but it often signals that no one has been running the system as a utility — and that the first year under new ownership could carry catch-up cost.

A worked example: pricing the compliance tail on a 150-lot park

The figures below are illustrative planning assumptions, not engineering quotes, and are not drawn from a specific transaction. Treatment and replacement costs vary widely with well count, flow, water chemistry, and local contractor pricing.

A 150-lot park, predominantly tenant-owned, served by two wells and a small distribution system. In-place Net Operating Income (NOI) of $600,000. Purchase price of roughly $8.6M, a 7.0% cap rate. The seller's T-12 shows about $18,000 a year of water system expense: electricity for the pumps, a contract operator, and routine sampling.

Now suppose the April 2027 monitoring comes back with PFOA above the limit, and an engineer's scoping estimate lands at $500,000 to $700,000 for centralized treatment, with $35,000 to $55,000 a year in added operating cost for media replacement, operator time, and expanded sampling. Using the midpoints:

The line item most models miss is not the capex; a buyer can negotiate that. It is the recurring cost, because it is capitalized. At a 7.0% cap, every $10,000 of permanent water operating cost removes roughly $143,000 of value. In the no-recovery row, the ongoing cost alone accounts for more than half of the combined hit.

That is why the recovery assumption carries so much weight. Whether treatment costs can be billed back to residents, and on what notice, varies by state — the same caution raised on utility billbacks in the MHP expense underwriting post. Where rent or utility pass-throughs are regulated, the no-recovery row may be closer to the truth. The point-of-use row borrows EPA's own estimated savings range and is only as good as the state's willingness to approve that approach for the system.

Diligence questions a private-water park tends to raise

None of these are exotic. They are simply the questions a utility buyer would ask, applied to a park — and they fit alongside the items in an MHP due-diligence checklist.

• Classification and history. What is the system's public water system ID, how does the state classify it, and what does the state's violation and enforcement record show over the last five years or more?
• PFAS status. Has any PFAS sampling been done — under the federal rule, a state program, or EPA's Unregulated Contaminant Monitoring Rule? If not, can pre-closing samples be drawn and run by a certified lab? And if the proposed two-year exemption is finalized, has the current owner requested it, and does the request transfer with the system?
• Service line inventory. Does a lead and galvanized service line inventory exist, and how many lines are listed as "lead status unknown"? Unknowns tend to be where replacement budgets are underestimated.
• Operator and permits. Is there a certified operator of record, are the well permits current, and who holds the relationship with the state?
• Municipal alternative. Is a public main close enough to connect? Tap fees, impact fees, and extension costs may vary by an order of magnitude between jurisdictions and are worth pricing directly with the utility.

Findings from these questions typically belong in two places: a price or credit negotiation, and a reserve line in the underwriting that is separate from general capex. Folding water compliance into a generic per-lot reserve tends to understate it on exactly the parks where it matters.

Where this thesis breaks

Three places, honestly.

First, many private-water parks may test clean. PFAS contamination tends to cluster near specific sources — airports, military installations, industrial sites, and some agricultural land — and a well far from them could well come back below the limits. The scenario table is a stress test, not an expectation; running it on a park with no plausible source nearby may overstate the risk and cost a deal that works.

Second, the rules themselves are moving. The 2031 extension and the rescission of the other four PFAS limits are both proposals, and litigation over the 2024 rule has been ongoing. A final rule could be looser than the one modeled here, or states could hold to stricter standards of their own. Underwriting to the rule as proposed, rather than as final, is a judgment call worth naming in the investment memo.

Third, a private system can be an advantage. A well-run, compliant system with a clean record and a recoverable cost structure may give an owner more control over utility expense than a master-metered municipal connection with escalating rates. The concern here is not private water as such; it is private water that has never been underwritten as a utility.

The Bottom Line

A mobile home park water system is a small regulated utility, and two federal rules now put dates on what that means: initial PFAS monitoring by April 26, 2027, and lead pipe obligations from November 1, 2027. The cost that tends to matter most is not the treatment plant — it is the permanent operating line it creates, capitalized at the exit cap rate, and how much of it the state lets an owner recover. Parks with private water may still pencil. The ones most likely to be mispriced are those where the test results, the pipe inventory, and the recovery rules were never asked about before closing.

For related reading, park-owned home expenses and infill yield on cost cover two other places where a park's T-12 tends to understate what ownership costs.

UWmatic is an AI-powered underwriting platform built for multifamily and mobile home park investors. Model water system compliance as its own capex and operating scenario, test how much recovery the deal needs, and see the value effect at your exit cap rate before the first sample comes back. Try the free underwriting calculator →

This analysis reflects current market interpretations as of the publication date and may evolve as new data becomes available. Regulatory figures are drawn from EPA and the Federal Register (the 2024 PFAS National Primary Drinking Water Regulation, the May 2026 proposed compliance extension and rescission rules, and the Lead and Copper Rule Improvements), with LCRI dates as summarized by the National League of Cities. The violation findings are attributed to an Associated Press analysis of EPA data published in July 2025, and the funding-confidence figure to the American Water Works Association as cited in EPA's proposal. The 150-lot park, its treatment costs, and its recovery assumptions are illustrative and are not drawn from a specific transaction. Proposed rules may change before they are finalized, and state requirements may be stricter than federal ones — verify current requirements with the state drinking water program and obtain engineering estimates before relying on any figure. Nothing in this post is investment advice; readers should conduct their own diligence and consult qualified professionals before making investment decisions.