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Fresh Water System Replacement Project


Mark Pearson
Staff member
We did a massive refit this winter of the fresh water system, new hatches for plumbing access, UV water filter, sinks, water heater, composting toilet, cockpit and anchor fresh water wash-down gear. Almost all of the old grey polybutylene was replaced, mostly with 1/2" PEX piping, widely available at any plumbing/hardware/home improvement store.

  1. Working with electricity can kill you or someone you love. If you don't know what you're doing, get a professional electrician to help.
  2. Working with fittings and pipe, especially below the water line, can sink your boat. If you don't know what you're doing, consult with an ABYC-certified technician.
  3. In my previous life, I was a registered Civil Engineer (PE) and I designed/built water/wastewater systems. But I also do more stupid things than an average person and some of the following ideas might be straight-up dumb.
I'll talk about the fresh water system in this Thread, and make other threads for the composting toilet, details of the water heater, UV water filter, cockpit and anchor wash-downs.

Mark-In-the-Box: getting to some of these parts was challenging for a "not small" person.


It is HIGHLY satisfying now that it is done, but it was a LOT of work, and I spent most of the winter doing it on weekends. I probably did 20-30 runs to Home Depot, Lowes, West Marine. I don't think I would tackle a job like this if I was not so close to a Home Depot, Lowes, or a big hardware/plumbing store. Even with lots of planning, there were always many unforeseen things I needed. We also live 7 minutes from where our boat was moored, and I happen to have almost every tool known to mankind. Those things helped too. ;)

Here is what my finished system looked like. Photo taken from the galley sink, with galley sink removed.


Okay, it looks a bit like Frankenstein, but I couldn't figure out how to make it lay out any cleaner.

Below is a photo with the parts labelled.


The little arrows above show the usual flow directions of the water. And here is a key to what those things are:
  1. Main access door under galley sink, facing aft
  2. New access door under galley sink, facing forward, behind seat-back cushion
  3. Valves to control flow from water tanks. 3a is from V-Berth tank, 3b is from starboard tank.
  4. Preliminary screen filter (part of JABSCO Ultra Max)
  5. Water Pump (part of JABSCO Ultra Max)
  6. Accumulator/Hydro Pressure Tank (part of JABSCO Ultra Max)
  7. Advanced Pre-filter for UV Filter
  8. UV Filter. 1/4" outlet port is under this label and runs to the UV Filter faucet on the sink
  9. Valves/Stub-outs to feed main galley faucet. 9a is cold, 9b is hot.
  10. Thermostatic mixing valve. See description below. Note from the Future: this is not a good idea and I took it out, see description below.
  11. Hot water tank outlet. There is an anode inside the outlet we need to check each year, requiring access to this port.
  12. How water tank blow-off valve. Discharge tube runs to bilge.
  13. Valves for controlling flow to cockpit wash-down. Can blend in some warm water or turn them off.
  14. Tee which feeds 1/2 tube to cockpit wash-down.
  15. Engine hot water inlet/outlet for hot water heater heat exchange
  16. Hole thru which pipes (hot and cold) run to the Head, and run from the shower drain, and from the V-Berth water tank.
  17. Hose bib (not fully visible in this shot). For draining system, running hose, pressure gauge, etc.
  18. Drain hose for galley sink. Goes to 1-1/4" through hull.
  19. Circular black Access Plate for access to water heater's thermostat and heater element for maintenance.
  20. Drain pipe, white 1/2" PEX from Head Shower.
  21. Brace/Bracket to secure upper water heater body.
Why Did We Do This?
  1. We had tons of leaks, and we couldn't just leave the water pump on: it would constantly cycle and drain the water tanks into the bilge via leaks. We found and repaired some leaks but couldn't find others.
  2. We didn't have any sort of Hydro/Accumulator tank to buffer the flow. So any time you opened a faucet for even a tiny bit of water, the pump kicked on.
  3. The old grey polybutylene pipe has a storied past. It was widely used in the 1980s, very fast & easy to install, flexible, etc. But it developed tiny cracks and leaks. You can imagine what a mess that was behind sheetrock in houses. So it was also the subject of one of the biggest class action lawsuits from homeowners seeking reimbursement. As it happens, most of our leaks were in old iron/metal fittings, but since I was ripping everything apart, I wanted to replace it.
  4. We wanted to add a UV water filter so that we could still take on water from unknown sources in other countries, and generally not need to worry about drinking it.
  5. Our existing water heater (original, ~40 years old) was pretty much disintegrated and leaking. When I put a pipe wrench on it to take it apart, I didn't even apply any pressure and it crumbled apart and drained the tank into the bilge.
  6. We often had scalding hot water (over 190 degrees) spurting out of our spigot. Because the tank is also heated by the engine, when running. We installed a thermostatic mixing valve so that no matter the temperature in the tank, the water (theoretically) gets equalized to a consistent 120 degrees.
  7. The ~40 year old sinks and fixtures were corroded and leaking, and replacing gaskets could not fix them. It was deeper than that.
  8. We hadn't used the saltwater pump at the galley sink in our 10 years of cruising on Zia. In addition to trying to reduce the amount of salt inside the boat, the underwater intake for this faucet was also right next to the head discharge (a.k.a. raw sewage), which does not seem like a good idea for rinsing dishes after you wash them. Also, the line to feed this faucet runs from the head to the galley well below the waterline, and is made out of the famously leaky old grey polybutylene, which does not seem like a good idea from a "sinking the boat" perspective. Anyway, we were not fans and it was taking up space on our sink, and we wanted it gone. Reasonable people do disagree with this.
  9. We had also never used the manual hand pump for water, and it was taking up space on our sink. We always have a spare water pump aboard, and we can always siphon water out of the tank if both pumps fail or there is no electricity.
Even with those fairly compelling reasons, we probably would not have taken on this project if it wasn't for the fact that we've been working on Zia for 10 years and have already done a ton of other "more important" projects. This was one of the last big things that we could do ourselves. We also had fun doing it and enjoyed the challenge. I don't think we would have taken this on if it wasn't fun/rewarding for us.

Why PEX Piping with Push-On Fittings?
There are other alternatives that would have worked fine. And reasonable people will disagree. I chose this because:
  1. It is super widely available (including other countries) and it has been used a lot over 20+ years.
  2. The piping is quite cheap, and it doesn't corrode.
  3. The push-on fittings cost a bit more, but I could barely reach most of these places. More elaborate fittings that required two hands or special tools were not as practical.
  4. The push-on fittings are also (sort of) easy to remove, so it is easy to change your mind on how you want to do something. Which I did often.
Feeding the PEX into the long run from the galley sink to the head. I went from the quarter berth, into the door under the galley sink, and into the hole that leads forward. This let me get the > 10ft segments installed as 1 piece.

I did not exclusively use PEX. I used the clear, flexible PVC tubing several places because:
  1. Some runs of the old grey pipe would have been very difficult (impossible?) to do with PEX because of twists, turns, corners that the old pipe made behind cabinetry and flooring (sole). It would have required sawing, drilling of cabinetry, or tearing up the sole. None of which I wanted to do. Example: from the head to the tank under the v-berth. I used a wire snake to get PVC tubing into that run, replacing the old polybutylene.
  2. I also used the PVC tubing in several places because it would make maintenance easier in the future. In the photos you can see several places under the galley sink that I used it for this reason. That was a personal choice with debatable payback, but I'm happy with it.
All of our old grey polybutylene has been replaced with one exception: the feed line from our starboard water tank to the valve under the galley sink is still polybutylene. It is a short run, and it is *not* under pressure, because it feeds the pump. So I'm not worried about it leaking. That line makes so many twists and turns I'm afraid I won't be able to pull replacement tubing. And if I can't do that, I'd need to tear up the sole, which I don't want to do.

Why a UV Filter?
I've been drinking water straight out of boat tanks for 30+ years. I probably occasionally got sick because of this, but I don't remember any specific times. I did get amoebic dysentery once in Spain. While it had a different cause, I'm not eager to repeat that experience. We plan on doing more voyages out of the country, and we want to not worry (too much) about water sources. Once in Thailand we saw a scummy livestock pond that fed the water pipes which ran out to the docks. With this system we have at least it removes the danger of that situation.

We eventually plan to install a watermaker, but even with very clean water in tanks, crud, bird poop, bugs, get washed down into tanks. For our drinking water, we wanted something better.

I'll do a separate thread about our rationale and alternatives we considered, but we ended up installing a UV water filter. It zaps & kills viruses/microbes/bacteria, etc. There is an 'advanced pre-filter' which strips out "lead, heavy metals, chlorine, mercury, carcinogens, and other contaminants, as well as turbidity, unpleasant odors and tastes.". The bottom line is the water that comes out tastes really good and is pretty darned safe.

We settled on an Acuva ArrowMAX 1 UV-LED because it is compact, has low power consumption, and a dedicated faucet with a light that turns on so you know the UV filter is engaged under the counter. The model we got is not super high rate of flow, but we just put our water bottles under the faucet and let them fill while we are doing other things. We recently had been getting our potable water via plastic bottled waters from the store. This helps us reduce "single use" plastics.

What the Heck is a Thermostatic Mixing Valve?
Note from the future: This is not a good idea, and we took it out. I think it would work fine under constant pressure. However, when when the water pump kicks on (and the pressure increases), it sends a very cold burst of water through the system. It still eliminates the 'scalding water' issue, but makes showering too thrilling.

Old Note (before we used it much): We used to have scalding hot water (190+ degrees F), out of our faucets. This is because when the engine is running we have engine water heat exchanging with the hot water heater. When the engine wasn't running, our water was around 140 degrees using electricity for heat. Nowadays, the accepted "non-scalding" temperature for hot water is around 120 degrees.

To accommodate the varying temperatures in the tank, I'm trying a "thermostatic mixing valve". This valve mixes cold water with the hot water from the tank to put out a consistent 120 degree water. It adjusts "on the fly". Further - it functionally expands the size of the tank because you can set your tank thermostat to the higher side (like 180 degrees), and you get a lot more water out of it at 120 degrees, once it mixed.

On our boats, because of the variations in the temperature of our water heater's water, and the size limitations, it seems like a perfect place to use of thermostatic mixing valves: making the temperature consistent and increasing the volume. I've never seen them used on boats, and I'm not quite sure why. I guess we'll find out.

Cash Acme Thermostatic Mixing Valve
I got a Cash Acme 3/4 Inch Tank Booster Water Heater with Thermostatic Mixing Valve. It also has an integral check valve for the water heater's inlet, and it is adjustable so you can increase or decrease the target temperature. https://www.amazon.com/gp/product/B00FBP2IPO/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

JABSCO's Ultra Max Model No. 59451-1012
I wanted all of these items, and JABSCO has them all in one unit:
  1. Screen Filter before the pump. Keeps big things out of the pump, and keeps them from damaging the pump
  2. Water Pump
  3. Pressure Switch to keep the system operating between 20 and 40 psi
  4. Accumulator (hydro pressure) tank. Many boats like ours don't come with these. It is essentially a small tank that is filled with air that is separated from the water with a diaphragm. It acts like a little buffered storage area. So if you open a faucet to fill a cup of water, the pump won't necessarily kick on.
All of the parts are modular, so I can swap them out if something fails.

Here is a close-up of the unit.


Head Plumbing

Obligatory before/after photos.
BEFORE: This is the plumbing inside the head vanity. I think this is all original 1983 piping. The mold is probably newer, though.


AFTER: Inside the head vanity. All the sewer piping is GONE because we now have a lovely composting toilet.

Labels Under Head Sink.png

  1. Hole which leads to path to the galley sink, under the port settee. Hot & cold feed lines to the head, leaving the head are the shower drain line (white), and the feed line from the v-berth water tank to the galley sink area. Also passing through here: v-berth tank level sensing wires, USB charging port wires, and wires to eventually power our (future) watermaker.
  2. Air ducts for our heater - Webasto diesel forced air.
  3. Exhaust air lines for the composting toilet, which goes outside through a clam-shell vent on the cabin side.
  4. Drain line for sink in head
  5. Shower drain pump. Pumped aft and into torpedo tubes in stern.
  6. USB & cigarette lighter port wiring for ports in cabin.
  7. Through hull valve, 3/4", for sink drain
  8. Through hull valve, 1-1/4", for removed toilet. Plugged with bronze plug.
  9. Through hull valve, 3/4", feed water for removed toilet. Plugged with bronze plug, but we plan to use this as feed water for future watermaker.
  10. Floor plate I made out of King Starboard to make a floor by the cabinet hatch
  11. New access hatch


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Mark Pearson
Staff member
The hot water heater that we chose was a Raritan Model 170611, 6 gallon with Heat Exchanger for engine cooling lines. I bought it through Defender.com.

I'll do a separate thread about the water heater.

If you are considering this heater, realize that it will not fit through the cabinet opening above the water heater. I had to install it through the sink opening. And if I ever need to remove the unit, I'll need to take the sink out, which is not a big deal (anymore).



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Mark Pearson
Staff member
This is what the galley sink looks like now. The smaller spigot is for the UV-filtered drinking water.
It's big enough that my wife can take a bath in it. ;)



Mark Pearson
Staff member
This is what the head looks like now, with new sink/faucet, hatches, composting toilet.
I'll do a separate thread about the composting toilet.


Warren Holybee

Active Member
Very nice work. I like what you did in the head, the sink and especially the new waste basket. Your plumbing is art work.
When I replaced my water heater, the Raritan fit through the top. It was replacing what I think was the factory Raritan of the same size. 382 hull # 256.
I could never give up a deep 2 tub sink in the galley. Mine is getting old, and is seems there are zero options for a like sized deep 2 tub sink. :(


Mark Pearson
Staff member
Hi Warren- interesting. Morgan must have sized the opening for the heater they were using on particular builds. Our old water heater was square & made by American Appliance (out of business).

The iron piping was so corroded that when I set a pipe wrench on it with no pressure, it disintegrated & drained the tank into the bilge.

Yeah, I’m happy with that trash hatch for the head. There is a trash can hanging in a basket below the metal hatch. Changing the trash is super easy, and the basket unclips for full access to the piping below in a few seconds.


Terence Thatcher
Mark, Adavida still has much of the grey,plastic pipe. I have never suffered leaks except when a fitting got loose. Was your pipe actually cracked? I have recently read, however, that any boat with a hot water system needs an accumulator tank to absorb expansion and I have always had one. Maybe that saved me. I would be interested to learn if others have had failures. Your work is stupendous.

Warren Holybee

Active Member
I have all the original gray pipe. I had intended to replace it, and bought a bunch of PEX, but ran out of time and it's all in storage. It's on my list. I never had any of it break. I tried to break some old pieces and it will, but it has quite a bit of give and flex before it does. I bought a selection of pieces to repair and keep it up while cruising, all the same grey stuff as it's still available. I replaced the metal ring and compression ring on a few fittings that leaked a bit. I had a couple failures of fittings, where the nut broke. Once was on the starboard water tank. Thank goodness for having a second tank and keeping them full, as I lost 30 gallons of water to the bilge while I was in Indonesia. And thank goodness for my having bought a bunch of spares because it would have really been a hardship with only one tank.

I also replaced the valves under the sink, as they didn't seal well anymore. If one tank was empty, I would just get air, even if it was closed.

My biggest concern with the grey pipe is the feed to the saltwater pump at the sink. That is a long run of the stuff, with several junctions below the waterline. The original foot pump sprung a leak in Fiji, and I had to close the through hull to stop it and use only fresh water until I got to New Zealand. If/when I get a watermaker I might do away with it, but for now having a salt water tap is critical to conserving water for a long passage.

The factory install of the hot water heater did not have an accumulator. That is verified on the drawings. The instructions for the new tank did say it was mandatory, but it would have made the installation too complicated for the time/situation. It has not been a problem. Some hot water gets through the one-way valve back into the cold water system from a "cold start" of the hot water heater.

I did install valves to isolate the hot water heater, both on the hoses to the engine, and the water into the heater. I leave it off unless I expect to shower.


Mark Pearson
Staff member
Yeah, Warren, having the old grey polybutylene below the waterline seems like a big concern. But I think because it’s not really under pressure (maybe 4 ft of head, or 2 psi) it hasn’t been a big problem. And I don’t think it has sunk anyone’s boat from what I can tell. Still, I’m happy to be done with it.

Terry - I guess the old polybutylene formed “hairline” cracks that leaked under pressure. I didn’t take a hard look at the pipe that I ripped out, but I think it probably had some small cracks. However I think our most major leaks were on the black iron connections that were around the old water heater. Because our new water heater has an anode I can inspect, we are hoping to avoid that going forward.


Beautiful work, Mark. Not only is your work extensive, it shows professional workmanship. Thanks for posting all of the details as this is helpful for those of us who venture down your various paths.

I have a fairly specific plumbing question for anyone on the Morgan38 site with regard to the grey polybutylene fittings.

I removed our galley faucet today. However, as I look at installing a new faucet I am not clear what fittings are necessary to connect the polybutylene (which previously directly connected to the faucet) to a new faucet. At first, I thought I could just use a Sharkbite from Lowes (polybutylene to PEX) then make the further necessary transition to the faucet. However, I now understand that we have 3/8" polybutylene, not the 1/2" size, for which Lowes sells a Sharkbite transition.

How does one connect to the polybutylene - maybe onto Pex or something more modern (and ultimately to the galley faucet)?

Thank you for any guidance on this specific.

Warren Holybee

Active Member
The gray tubing has an inside diameter of 3/8" However, the outside diameter is the same size as the od of 1/2" copper pipe. (slightly larger than 1/2")

What this means is that it is compatible with 1/2 " copper thread fittings. A new faucet, made for 1/2" copper pipe, will work perfectly with the nut fittings on the gray pipe. No adapters needed.

I hope that makes sense and answers your question.


Thank you, Warren, for your explanation. That makes great sense and it is great news. The new faucet work (among many projects) can now proceed. I appreciate the help!


Mark Pearson
Staff member
Hi Maurice - I'm pretty sure what Warren says is true. That would be more elegant than dealing with adapters, etc. I would double check that with my calipers for you, but we are traveling until Tuesday.

I used a special adapter to go from the 3/8" grey polybutylene to 1/2" PEX.

This worked very well for what I was doing: https://www.amazon.com/gp/product/B000BQU3Y6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

You can see it in the above photo - it is below the valve labelled 3b in the photo under the galley sink.

Good luck with your plumbing endeavors!


Right on Mark !! I’m undergoing the same project here. I decided to replace the poly all the way to the tank and went with flexible hoses to the water pump and the manual hand pump.
One thing that’s key for me is that I a lot of valves that allow me to isolate each line should there be any failures.
So basically everything under the sink for me will be flexible, and starting at the water heater to the head will be PEX. I’ve already converted the head and shower to pex last year so I’m just hopeful it won’t be a pain in the ass to get the pex from the galley to the head.

Good work btw!!!


Mark Pearson
Staff member
I just amended my original post in this thread to say the Thermostatic Mixing valve didn't work as expected.

We have been super happy with our new plumbing, and everything works great. With the exception of the Thermostatic Mixing valve. I think it would work well in a constant pressure system, however our water pressure varies a lot when the water pump kicks on. When that happens a jolt of very cold water gets sent thru the pipes. I guess it makes sense because the mixing valve is passive - I can see a pressure spike would push some extra cold water through.

Anyway, we removed the mixing valve. No bueno, and I wouldn't recommend it.