Material for fresh water tank


Gotta Be Nuts
Hey all, I am getting to the point in our build that I need to get a water tank. I will likely get a custom tank to fit the space to get maximum volume. The question I have is this, what material would you recommend the tank be made out of? Polypropylene, HDPE or 304 stainless? Years ago we had a sailboat with a white plastic water tank (not sure what is was made of) that gave the water a plastic taste. Our current boat has stainless but if the water sits a while you can taste rust. The reason I say this is I would like to have as little added taste to the water as possible.
304 stainless should not have a rust taste. If it does someone has used a black iron pipe fitting somewhere. Stainless to stainless or it must be galvanic isolated.

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I built mine from 304SS. It's external and probably subject to hitting rocks and such at some point so I made it from 1/8" thick plate. The plate was also given to me by a friend so that was nice but I would have spent the money anyway. It's around 65 gallons I believe.


Gotta Be Nuts
Thanks guys, just got some rough estimates back from both plastic ($1k to $1.5k) and metal tank builders ($2.5k +). Due to budget we will go with a plastic welded tank. From what I have been told by the builders is with plastic welded tanks you can have internal baffles. Our tank will be just over 100 gallons so I want a couple of baffles in it. So now the choice is between polypropylene (what one tank builder recommends) and HDPE (what the other tank builder recommends). Both are recommending 1/2" thick walls so it should be pretty stout.

About our current SS tanks, they are 30 years old and we used a R.O. unit to fill them while cruising. So there is always trace amounts of salt. The rust is not a huge deal but one thing I have learned sailing on oceans is that all SS will eventually rust.


Active member
Yes, on a boat I’d use 316 at least...

For your current tank project, polypropylene is what I’d use.

Reach out to U. S. Plastics and see what they have or can make for you. They did some tanks for us (PP and PE) for a nitric acid strip installation. Pricing was much better than the local fab shop.

If they have something pre made, that’ll be even cheaper.


Engineer In Residence
Instead of welding one large tank, I would consider having two or three smaller tanks rotomolded from polyethylene or polypropylene. It may cost less overall , and you will end up with the system more tolerant of leaks that won't need baffles. The fittings will be spin welded on.

Obviously you will need a couple of valves to allow you to isolate each tank .


I second luthj when he says multiple smaller rotomolded tanks. I like PE, but thats just me. There is the redundancy of multiple tanks, it removes the need for the baffles, there are plenty out there to choose from, and you always have the option of filling one up with questionable water, then pumping from it through filtration to ensure it is potable should such an emergency arise. You would only have one tank to sanitize vs. an entire system.

Two sources I have used for various projects are and I have had better experience with the former, especially when having them install the fittings where I wanted on a custom unit. I should say the tank was a generic size that they have, but the fitting size, quantities, and locations were all where I specified. All spun weld, so fittings simply screw into place.


Gotta Be Nuts
Hey guys, one of the issues with getting a generic sized tank is my habitat design and where I want to place the tank. If you look at the front wall you will see a small angle there. That is in place to allow the cab to flip up and get the box as close to the cab as possible. Seemed like a good idea at the time but has added a lot of work compared to a regular box. Anyway, in order to get the maximum amount of water for the available space the bottom front edge of the tank will have to match that angle and then go vertical. I'll inquire about the cost difference between 2 smaller tanks and one larger one with baffles. The only custom tanks I have found are welded and not rotomolded.



Engineer In Residence
I have not done it personally but there are a few companies that do custom rotomolding. It May be worth a quick Google search.


Active member
For a custom, welding is where it’s at. You might find a rectangular design that can have the lower corner clipped but for maximum volume in minimum space a single baffled tank is the option. Not that the other ideas don’t have merit, just I e been down this road myself...

You might consider welded stainless steel as well. I made a cardboard mock-up and had a shop make it. It was a strange shape in my case to fit behind the left rear wheel and it came out great.


This guy saved the day when I ran over somebody’s trailer hitch at 65 on a freeway. Put a hole in my fresh water tank about the size of a.... tow hitch.

He welded up a fix in minutes. He does custom tanks too. Don’t know him personally, but he really appeared to know what he was talking about.

Not sure how shipping or new build quotes would go, but maybe check out his website or give him a ring. He’s located in Detroit, Michigan.


Tea pot tester
I had some plastic tanks made up a while ago, three tanks totalling about 100 US gal. Sized to go though the door :)
I asked for some connections to be fitted during construction but that was a mistake, what I imagined was a good idea at the time turned out to not be ideal once other stuff became more fixed. Even for instance having a threaded nut welded in to take a 40mm 90 degree bayonet fitting for filling, but once the thread is done up tight it faces the wall no room for pipe. Theres only so much ptfe I can wrap to change it's done up direction.
I could then have maybe had no holes except at the top for filling, drawing, cleaning, level sensor and a vent, so less chance of a leak?
The back wall of each extends about an inch higher than the top to allow screwing to the wall, same with the base pieces.
Our plan with three tanks is two fillable from outside, the third is filled by filtered output from one and two. Everything inside is then only fed from the clean water tank. If the two tanks are full we can then filter into the third at leisure rather than fill speed being restricted to filter throughput. We're filtering everything because our son is too small to trust not to drink from the shower etc, otherwise just a filter tap would do.
If you had square sided tanks made that don't fit the front wall profile could you make use of that gap for maybe water filters, pump, other bits that don't mind being hidden, perhaps on a board you could lift up and out with everything mounted on that for access? All that junk takes up a lot of room!

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Im also researching water tanks and need 100 gallons for my 7x16 trailer. I want them under the floor.

Sure would be nice to find and buy some premade 50 gallon tanks that were designed to set between floor joists..