Fresh Water Line and Leak Repair on RVs, Trailers and Vans
Written by RV Systems Lead, RV Systems and Electrical Lead, OCRV Center. Reviewed by Claims Coordinator
In shortA pump that will not settle overnight is proving a leak exists somewhere downstream. Pressurized side work runs $285 to $4,500 at $260 per hour, with location time billed at the diagnostic rate.
How is a fresh water leak located and repaired on an RV?
Fresh water line repair covers the fill, tank, pump, supply runs and every fitting carrying pressure. Rancho Santa Margarita owners bring the unit to Yorba Linda, where it holds regulated city water on a decay gauge, gets isolated zone by zone, and the failed joint is remade in material matched to the coach.
- Polybutylene insert fittings go brittle with age and let go without warning
- A pinhole usually sits where a line crosses a frame member unbushed
- City water inlet check valves fail and push tank water back out the fill
- A low point drain left cracked open reads as a dead pump
- Price range
- $285 to $4,5001 to 18 labor hours at $260 per hour
- Labor rate
- $260 per hourMechanical and electrical department
- Leak location
- $285 per hourOne hour minimum, credited in full against an authorized repair
- Typical turnaround
- 1 to 5 shop daysLonger where flooring lifts to reach a run
- Written estimate
- $150Credited in full against an authorized repair
- Tubing handled
- PEX-A, PEX-B and original gray polybutylene
Last verified
The pressurized half of an RV water system is the half that causes damage. Everything from the city water inlet to the last tap sits under thirty to sixty pounds of pressure for as long as the pump is armed, which on a coach parked in a storage row can be months. A joint that weeps one drop a minute under that pressure moves close to forty gallons a season, and almost none of it lands anywhere you would notice.
So the real question is never where the water is. It is which joint let go, what generation of plumbing this unit carries, and how much decking has already turned to sponge on the way down. Only the first of those three is about plumbing.
What a fresh water fault looks like before you find water
The first sign is almost always the pump, and it is easy to miss because it happens at night. Arm the pump with every tap closed and stand still. A healthy system builds pressure, the pump stops, and it stays stopped. If it wakes up for a second or two every few minutes, water is leaving the system somewhere and the pump is topping it back up. That is not a switch problem and it is not normal behavior for an accumulator.
The second sign is smell before stain. Wood that has been damp for weeks smells before it discolors, and the smell concentrates inside a closed base cabinet where air does not move. Owners describe it as musty or as an old wet towel. Open the cabinet under the galley sink, put your hand flat on the floor at the back corner, and compare it with the front. A cold, slightly soft patch at the back is a finding.
- Pump wakes briefly every few minutes with nothing running
- Pressure drops off a second after a tap opens
- Musty air inside a closed cabinet with no visible stain
- Mineral crust or verdigris on a fitting behind a panel
- Tank level falling while the unit sits on a park hookup
Polybutylene, PEX and what the model year predicts
Ask what your unit was plumbed with before you form an opinion about its reliability. Coaches from roughly the mid nineties back through the seventies commonly carry gray polybutylene tubing on acetal or brass insert fittings. The tubing itself is often fine. The fittings are the problem: they lose plasticizer, go brittle, and split along the barb where the tube is stretched. They fail without a warning weep, which is why polybutylene failures tend to be floods rather than drips.
Units built over the last fifteen years or so are predominantly PEX, which is a genuinely good system with two failure points. One is workmanship, where a crimp ring was set with the wrong die or not fully closed. The other is abrasion, because PEX is soft and a run that passes through an unbushed hole in plywood will eventually wear through from the outside. Neither is a material defect and both are repairable to better than original condition once the crossing is protected.
| Era and material | How it fails | What the repair usually is |
|---|---|---|
| Gray polybutylene, acetal inserts | Sudden split at the fitting barb | Rebuild in PEX or replace the affected run |
| Early PEX-B, copper crimp rings | Weeps at an under crimped ring, often only when hot | Cut out and recrimp with calibrated jaws |
| Modern PEX-A, expansion rings | Abrasion pinhole at an unbushed crossing | Section replacement plus grommet and clips |
| Mixed eras joined with push fittings | Leaks at the transition, usually inside a wall | Remove the transition, run continuous tubing |
Crimp, expansion and push fit: which joint belongs where
A crimp ring squeezes the tubing onto a barbed insert and is the standard in RV production because the tool is cheap and the joint is compact. Done with a calibrated jaw and checked with a go/no-go gauge it is reliable for decades. Done with a worn tool it holds cold and weeps hot, which is the single most misdiagnosed fresh water fault we see, because owners run the pump cold at home and find nothing.
Cold expansion stretches the tubing itself over a rigid fitting and lets it shrink back, which makes the tube the clamping element. It is the strongest of the three and it needs room to swing the tool, so it goes where access allows. Push fit couplers seal on an internal O ring and a stainless grab ring. They are excellent for a repair behind a removable panel and they are the wrong choice inside a closed wall, because the one thing an O ring joint needs is the ability to be inspected.
Before you proceed
If somebody has repaired your coach with a push fit coupler and then screwed a wall panel over it, that joint is now unserviceable. We note those on the file and offer to relocate them while the wall is open for something else.
How the leak gets located rather than guessed at
Water travels along whatever is beneath it, so the wet patch and the failed joint are frequently in different rooms. Opening panels near the stain is the instinct and it is usually the expensive mistake. We work from the gauge instead. Regulated supply in, valve closed, pressure held, decay measured. That single test says whether a pressurized leak exists at all and roughly how large it is, which is information no amount of panel removal provides.
From there it is subtraction. Isolate a zone, hold again, and either the decay follows the zone or it does not. On most units the leak is inside a specific run within the first hour, and the fitting itself is often a part worth a few dollars. That is why leak location carries a diagnostic line at the top of the estimate: finding it is the skilled work, and remaking the joint is the easy part.
- Bring the system up on regulated supply and isolate it
- Measure the decay rate and record it
- Valve off zones in turn and repeat the hold
- Meter the surrounding structure before opening anything
- Open one access point, confirm the joint, rebuild it
- Hold cold, run the water heater, hold hot again
The city water inlet, the low point drains and the bypass valves
Three components account for a surprising share of complaints that owners describe as a leak or as no water. The city water inlet contains a check valve whose only job is to stop pump pressure escaping back out of the fill. When it sticks open the tank slowly drains onto the pedestal, which looks exactly like a leaking tank and is a twenty minute part. The pitted brass seat behind a failed valve is why we replace the assembly rather than the insert.
Low point drains sit at the bottom of the hot and cold runs and are meant to be opened once, at winterizing, and closed again. A drain left a quarter turn open weeps into the underbelly where nobody sees it and the pump runs forever. The winterizing bypass valves at the water heater are the other habitual offender: left in the bypass position, the heater sits empty and the coach delivers cold water from a working heater, which sends people looking for a gas fault that does not exist.
Why the invoice is mostly carpentry by the time you arrive
A fitting remade behind a shower surround is an hour of plumbing. The swollen cabinet base beneath it, the delaminated wall panel behind that, and the section of lauan decking that has been damp long enough to lose its glue line are finish and structural work, and on a coach that has been leaking through two seasons they are the majority of the bill. This is not an upsell mechanic, it is the physics of a lauan and luan-cored floor meeting water for months.
Which argues for acting on the small signal. A pump that will not settle overnight is a cheap problem. The same leak found when the floor gives way at the step is the identical plumbing job with a far larger bill behind it. Moisture readings are taken on every job here for that reason, and the damage is quoted separately.
What this costs, and why the unit has to be here
Fresh water work bills at $260 per hour from the mechanical and electrical department across a band of $285 to $4,500, with location time at the diagnostic rate of $285 per hour, one hour minimum, credited in full against an authorized repair. Parts carry standard markup, sales tax applies to parts and materials, and labor is not taxed. A written estimate is $150 and credits the same way. Jobs over $2,000 take a deposit at authorization.
This is not a mobile repair category and we do not do roadside leak chasing. Locating a pinhole needs a metered supply at a known pressure, a decay gauge, an isolation manifold and a drain we are permitted to fill and empty into. A garden hose and a flashlight in a storage row produce exploratory panel removal, which is the most expensive way anyone can approach a water leak. Owners from Rancho Santa Margarita run the 241 to the 91 and skip the surface streets entirely.
On cost
Where an older coach has had one polybutylene fitting fail, we quote the single joint and the full run replacement side by side. The second number is larger today and it is the one that stops the next flood.
Which vehicles we do this on
The failure profile shifts with construction. Trailers and fifth wheels hide long runs above an enclosed underbelly, where a weep can go a year unseen. Motorhomes put a pump, an inlet and a dozen joints in one wet bay box. Van conversions bury the system in cabinetry with no service access, and park models sit still long enough that a drip becomes structural.
What is included
- Regulated pressure hold with a decay gauge
- The unit comes up on metered city water, gets isolated and sits under a gauge. The rate of decay tells us the size of the leak before a single screw comes out.
- Zone by zone isolation
- Runs are shut off in sections and the hold is repeated, which narrows a leak to a length of tubing rather than to a room.
- Material and era identification
- We establish what the coach was plumbed with and note it in the file, because the repair for polybutylene is not the repair for PEX and the difference is thousands of dollars over the next five years.
- Moisture mapping around the suspect run
- Pin meter readings at cabinet bases, along the floor line and at the wet bay, recorded with locations so the wet area is documented rather than described.
- Grommeting and support of every run we disturb
- Crossings are sleeved and clips are added. A line that chafed once will chafe again if it is put back the way it was found.
- Heat cycled retest before anything closes
- Hot water is run through the repaired section and the hold is repeated warm, which is the only way an under crimped ring shows itself in the shop instead of in a campground.
How the work runs
Hold pressure before touching anything
45 minutes
The coach goes on regulated supply, the system is brought up and isolated, and the gauge is watched. A hold proves the pressurized side is sound and sends us to drains and seals instead. A decay tells us roughly how big the leak is and where to spend the next hour.
Isolate down to a run
1 to 3 hours
Sections are valved off in turn and the hold is repeated. On a fifth wheel with a wet bay, galley and rear bath this usually gets the leak inside a single length of tubing, which is far cheaper than opening cabinets in whatever order they happen to be easiest to reach.
Identify what the coach is plumbed with
30 minutes
Gray polybutylene with acetal inserts, early PEX-B with copper crimps, or modern PEX-A with expansion rings all fail differently and all need different parts on the van. We establish which before ordering anything, because a mixed era joint is the leak nobody finds later.
Meter the damage and quote it separately
45 minutes
Readings go on a sketch with locations. Swollen cabinet bases, delaminated panel and soft subfloor are finish and structural work, and they are priced as their own lines so you see the plumbing number and the carpentry number apart.
Rebuild the joint and protect the run
2 to 14 hours
The failed section is replaced in matched material, crimps are set with calibrated jaws, crossings are grommeted and clips added. Push fittings only go where a service panel keeps them reachable, never inside a wall that is about to be closed.
Hold cold, then hold hot
1 hour
The system is pressurized and held again, then the water heater is run so the repaired section sees hot water, and the hold is repeated. Ten quiet minutes with the pump armed and everything closed is what releases the unit.
What this costs
$285 to $4,500
1 to 18 labor hours at $260 per hour, mechanical and electrical.
- Parts at $100 or less carry 100 percent markup. Parts over $100 carry 35 percent. Special order parts require a full non refundable deposit at order.
- Sales tax of 7.75 percent applies to parts and materials. Labor is not taxed.
- A 50 percent deposit is taken at authorization on any job over $2,000, with an additional 25 percent when parts arrive on any job over $10,000. Final balance is due at pickup.
- A single accessible fitting located and remade sits at the bottom of this range.
- Replacing every gray polybutylene run on a large coach sits at the top.
- Finish and structural repair caused by the water is quoted as its own scope.
How estimating is billed
- Written repair estimate: $150, credited in full against an authorized repair.
- In depth diagnostic, scan and programming: $285 per hour, one hour minimum, credited in full against an authorized repair.
- In shop pre purchase inspection: $400 to $1,200 depending on unit size and systems count.
- Insurance walk ins are accepted during posted hours. All inspection and estimating work is performed in shop at the Yorba Linda facility.
What you will notice first
- The pump kicks on for a second or two every few minutes with every tap closed
- Pressure starts strong at a faucet then falls away after a few seconds
- One fixture runs weak while the rest of the coach is normal
- The fresh tank empties overnight while the unit sits connected to a park hookup
- A musty smell inside a base cabinet with no water visible anywhere
- White mineral crust or a green stain on a fitting behind an access panel
- Water dripping from the underbelly hours after the pump was switched off
- The floor immediately inside the entry step flexes under one foot
How this fails, and what we do about it
| Failure mode | How we diagnose it | The fix |
|---|---|---|
| Polybutylene insert fitting split at the barb | Pressure decays steadily rather than fast. The fitting shows a hairline running along the barb shoulder and the plastic snaps rather than flexes when it comes off. Common on gray line coaches past twenty years. | Cut the fitting out and rebuild the joint in PEX with a transition, or replace the whole affected run. On a unit that has had one of these go, we price both, because the rest of the fittings are the same age. |
| Abrasion pinhole at a frame crossing | The leak is intermittent and worse after towing. Following the run finds a flat wear scar on the tubing and a matching bright mark on the plywood or steel edge it has been rubbing. | Replace the damaged section, then grommet or sleeve the crossing and add a support clip either side so the run cannot move again. Patching without fixing the crossing is a repeat visit. |
| City water inlet check valve stuck open | The tank level drops while the unit is on a hookup, or water runs back out of the inlet when the pump runs with the hose off. Confirmed by capping the inlet and watching the tank hold. | Replace the inlet assembly rather than the valve insert alone. The brass seat is usually pitted by then and a new insert in an old seat leaks again within a season. |
| Under crimped ring on a hot run | Holds cold, weeps once the water heater has been on for twenty minutes. A go/no-go gauge on the ring shows it out of tolerance, which is a workmanship finding rather than a wear one. | Cut the joint out and recrimp with a calibrated tool, then heat cycle the run and hold pressure again before anything closes up. |
Why it happened
- Acetal insert fittings on original gray polybutylene lines going brittle from age and chlorine exposure, then splitting at the barb where the tubing is stretched hardest
- A PEX run that passes through a drilled hole with no grommet and has been sawing against the plywood edge every mile the unit has travelled
- Crimp rings set with the wrong die or only partly closed, which holds fine cold and weeps as soon as the water heater sends hot water through the same run
- A freeze split from a season the unit was not drained, which often shows up in spring at a low point rather than at the fixture
- An unregulated park supply, or a regulator that has failed open, putting park main pressure into tubing never designed to carry it
- A city water inlet check valve stuck open, so pump pressure pushes back out the fill and the tank drains itself down the pedestal
Parts and brands we work with
- Uponor and SharkBite PEX-A and PEX-B tubing in half inch and three eighths
- Copper and Oetiker style crimp rings set with calibrated Milwaukee and Rothenberger jaws
- Uponor ProPEX expansion rings and cold expansion fittings where the run is accessible
- SharkBite push fit couplers, used only where a joint stays reachable behind a service panel
- Flair-It and Sea Tech acetal insert fittings for original polybutylene runs that are staying
- Valterra and Camco city water inlets with integral check valves, plus Watts brass regulators
What not to try yourself
- Leaving the pump armed while you decide what to do. It is filling something, and every hour it runs adds to the carpentry side of the bill rather than the plumbing side.
- Putting a push fit coupler inside a wall or above a ceiling panel. It is a good fitting in an accessible spot and a bad one where nobody can ever check it.
- Sealing a weeping insert fitting with tape or a compound. Polybutylene fails at the barb, under the collar, where nothing applied outside can reach.
- Running a park hookup with no regulator because the water pressure felt normal. Pedestal pressure varies by time of day and a regulator is cheaper than a sidewall.
Which vehicles we do this on
Vehicles we perform Fresh Water System on
Travel TrailerTravel trailer repair covers A frame tongue welds, the front cap that takes road debris, the roof front radius seam, sidewall delamination starting at a window corner, and equalizer and axle wearStandardStandard fifth wheel repair concentrates on the pin box and upper deck welds, the floor at the step up transition, the front cap above the pin and the roof front radius seamClass A GasClass A gas motorhome repair covers the molded front and rear caps, the vacuum bonded laminated sidewalls, the EPDM roof and the F53 chassis underneathCamper Van ConversionCamper van conversion repair covers aftermarket build outs in bare cargo vans: Sprinter, Transit and ProMaster shells finished by a shop or an ownerPark ModelPark model repair treats the unit as a sited structure: frame corrosion and sag from years on blocks, pitched roof and flashing detail, residential window sealing, and moisture trapped behind skirtingVintage and ClassicVintage coach work means riveted aluminum or stick and tin construction over timber or steel framing, bedded in butyl rather than bondedI ask two questions before I look at anything: what year is the coach, and is the pump quiet with the taps shut. The year tells me whether I am dealing with acetal inserts that shatter or PEX that pinholes, and the pump tells me whether there is anything to find at all. On a gray line unit I will always price the whole run alongside the one fitting, and owners sometimes think that is upselling until I hand them the broken fitting and they see it snapped like a biscuit. Every other fitting in that coach is the same age and the same plastic.
Appendix: questions and answers
- How long should an RV water system hold pressure before you trust it?
- Fifteen minutes cold with the supply valved off, then again hot after the water heater has run. Cold only is not enough, because an under crimped ring seals when the tubing is stiff and opens once hot water softens it. Both holds have to be flat before the unit leaves.
- What is the practical difference between crimp, expansion and push fit joints?
- A crimp ring clamps tubing onto a barb and needs a calibrated tool. Expansion stretches the tube itself over the fitting and is the strongest of the three but needs swing room. Push fit seals on an O ring and a grab ring, which is fine behind a removable panel and wrong inside a sealed wall.
- Is it worth replacing every polybutylene run at once?
- Often, yes. Those insert fittings all left the factory together and they age together, so one failure predicts the next. We price the single joint and the full replacement side by side. Owners keeping the coach usually take the bigger number once, and owners selling within a year take the smaller one.
- Why does my fresh tank drain itself while I am hooked to a park pedestal?
- The check valve inside the city water inlet has stuck open, so supply pressure pushes into the tank or pump pressure escapes back out the fill. Cap the inlet and watch the level to confirm it. We replace the whole inlet assembly, because the brass seat behind a failed valve is usually pitted.
- Can a frozen split line be patched or does the whole run get replaced?
- It depends on how far the ice travelled. A single split in an accessible length gets a section replacement. Where a run froze end to end, splits appear at several points and often at low point drains, and piecing that together behind a wall is a false economy. We pressure test to map every split before quoting.
- Do I still need my own regulator if the park says its water is regulated?
- Yes. Pedestal pressure varies through the day and across a park, and a site regulator you cannot inspect is not evidence of anything. A brass regulator with a gauge costs less than one wall panel. A regulator that has failed open is a root cause we find behind burst supply lines several times a year.
Open a file on this repair
Tell us the vehicle, what happened and whether a claim is open. We will tell you what the scope looks like and what it takes to get you back on the road.
Or call (949) 799-3387