How to Estimate Water and Sewer Capacity Before Buying an RV Park

August 23, 2026 · RV park investing, explained

Public domain, via Wikimedia Commons

Water and sewer capacity is one of the most misunderstood parts of RV park due diligence. Buyers spend weeks modeling occupancy and ADR, then treat the septic system or well as a box to check off. Sellers rarely bring it up unless asked directly, because the system usually works right up until the week it doesn't. And a lot of parks were built decades ago under permitting rules that no longer match how the property operates today. That combination, buyer inattention plus thin paperwork, is why so many people close on a park and discover a capacity problem in their first busy season.

Before you get to the real process, it helps to clear out a few beliefs that sound reasonable but aren't.

"If it's working now, it'll work with more sites"

This is the most common one, and it has a kernel of truth. A system that is currently functioning proves the baseline isn't failing today. It does not tell you how much margin exists above that baseline. Septic systems, lagoons, and even municipal sewer connections are often sized close to the number of sites already built, especially in older parks that were expanded in phases without matching infrastructure upgrades. Add ten sites, a bathhouse renovation, or a laundry building, and you can push a system from adequate to overloaded. Overload shows up as slow drains, saturated leach fields, sewage surfacing after heavy rain, or algae blooms in a treatment lagoon. None of that shows up in a walkthrough during dry weather in the shoulder season.

"The county permit number is the real capacity"

The permit is a legal document, and you should absolutely pull it. But it's often based on design flow assumptions from whenever the system was originally engineered, sometimes 20 to 50 years ago. Those tables commonly assumed lower per-site water use than modern RVs with full hookups, washer/dryer combos, and longer average stays actually generate. Some parks also operate on grandfathered permits tied to a site count that no longer matches what's physically on the ground, because sites were added informally over the years without updating the paperwork. The permit tells you what the county thinks is approved. It doesn't tell you what the system can actually handle today, or what shape it's in.

"A septic or well system that passed inspection is good indefinitely"

An inspection is a snapshot. It tells you the system is functioning on the day someone looked at it, not how much life is left in it. Leach fields have a real lifespan, commonly somewhere in the range of 20 to 40 years depending on soil type, loading rate, and maintenance history, and that range is wide because local conditions matter a lot. Wells can decline in yield over time, particularly in areas under drought stress or where nearby agricultural or residential pumping has increased. A well that produced 20 gallons per minute five years ago might produce noticeably less now, and a single point-in-time flow test won't reveal a declining trend unless you can compare it against historical records.

What actually matters instead

The goal isn't to find a document that promises the system is fine. It's to build your own picture of current usage versus real capacity, using more than one data source.

• Pull actual usage history, not estimates: water bills, well pump run-time logs if available, and sewer flow meter readings where the park is metered.
• Compare that usage against design capacity. Design flow estimates for RV sites commonly range from roughly 100 to 150 gallons per day per site depending on hookup type, plus additional load for laundry, showers, and dump stations. Treat any number you're given as a range, not a guarantee, and ask what assumptions it's based on.
• If the park is on septic or a private treatment system, get a capacity and condition assessment from a local environmental or civil engineer. Ask specifically about the age of the leach field or lagoon, soil percolation history, and any prior repairs or expansions.
• If the park relies on a well, get a current flow test and ask for historical well logs. Where possible, talk to a local hydrogeologist or well contractor about aquifer trends in that specific area, since drawdown patterns are very local.
• If the park is on municipal water or sewer, contact the utility department directly, not just the seller. Ask about current tap allocation, remaining capacity in that service area, and what connection or impact fees would apply if you add sites later. Some municipalities cap new connections in certain zones regardless of what the property owner wants.
• Build in a buffer for peak season and any expansion plans. A system that handles average daily use fine can still fail during a three-day holiday weekend when every site is full and every guest is doing laundry.

None of this requires becoming an engineer yourself, but it does require asking better questions than "does the system work." When the numbers get close to the edge, or the park is older with thin records, that's the point to bring in a professional rather than guess. At Invest With Zac, this kind of infrastructure due diligence is treated as a first-pass filter, not a footnote, because it's usually cheaper to walk away from a marginal system than to rebuild one after closing.