Lining a solid watertank

[peterchech]

I plan on installing a plywood water tank under the cockpit floor of my boat. What should I line the tank with, that is non-toxic for drinking water? Is a plain epoxy coating OK for that, or are there special paints/liners I should obtain for the purpose?

http://i961.photobucket.com/albums/a...2211121601.jpg (a pic of the opened up space)


Just as some background, I priced some pre-made options, and the cheapest option is two 25 gallon tanks at $150 each. This is more than I want to spend. Plus, I like doing things myself.

I already have some epoxy, filler and fiberglass left over from another project. The plywood would cost me only about $60, so this could be a relatively low budget project.

I intend to make the watertank square, I think from 1/2 inch acx epoxy coated plywood. The interior of the tank will be lined with 4 oz woven fiberglass, taped at the edges with 6 oz tape. The baffles will be an X-shape inside, either of 1/4 inch ply or 1/2 inch, not sure about that yet. The criss crossing baffles should add some structural strength to the tank. I am still unsure how I will attach the tank securely to the hull, but I am considering glass taping it in.

[bljones]

Here you go:

http://www.epoxyworks.com/18/pdf/tanks.pdf

[JedNeck]

Have you looked into a bladder?

[RichH]

The recommendation of 'epoxyworks' is a good one and highlights (slightly) the strategic disadvantage of using epoxy (and other polymers) .... incompatibility for usage in POTABLE water service .... continual 'chemical emissions' or continual 'leachables' that would GREATLY exceed the standard 'food grade' or FDA regs. for potable water service. The usage of 'polyester' would be magnitudes 'worse' (as is found in many 'production boat' tanks).

To get to at least an emissions level that approaches 'safe', I strongly suggest that you 'overlay' the interior surfaces with a LOW AMINE epoxy that is 'targeted' for potable water service. An example of a easy/DIY 'roll on' NSF-approved potable water service epoxy would be: http://www.nsp-specialty.com/pdf/120nsftds-07.pdf
Even with a low amine coating in a water tank it would be prudent to add a carbon filled filter, and 'recirculate' the tank water through the carbon packed filter for an hour or so to 'strip' out the eventual 'leachables' before using to drink, etc. This recirculation-filtration probably should be done anytime that the boat hasnt been used for 'more than a few days'.
Simply adding a carbon filter to a spiggot isnt going to get you to 'safe' when it comes to 'leachables'.

You will have 'very great difficulty' in finding a 'bladder' that is NSF certified for 'potable water service'. Dont put your liver at high risk !!!!!!!

[Ritchard]

If you choose to build a wooden tank, I wonder if half inch ply is stout enough material if you have a full water tank, and the boat gets tossed around some. I think I'd want heavier stock.

We have a bladder that I recently installed on our boat, but we don't drink it. We prefer to bring along a supply of either bottled water, or a 5 gal water bladder. This is in part because the freshwater plastic piping on my boat is 30+ years old, I don't trust it, and haven't got around to replacing it.

[peterchech]

Only places I could find the nsp 120 online was here:

http://www.epoxyusa.com/ProductDetai...field+below%2E

and here:

http://www.king-cart.com/cgi-bin/car...ct_match=exact

I've never ordered from these places before so I don't know how good they will be about delivering on time and whatnot.

It does say though, potable water approved for tanks over 1000 gallons. Wouldn't that mean it is not approved for my little 40 gallon or so tank?

[bljones]

First of all, why the hell do you need, or want, 50 gallons of water on a coastal cruising boat?
10 gallons is more than enough for a weekend, 25 gallons will last you through a week long cruise for two.
Buy two 5 gallon jerry cans at $10 each, install some padeyes to attach hold down straps, and call it done.

[peterchech]

Originally Posted by bljones

First of all, why the hell do you need, or want, 50 gallons of water on a coastal cruising boat?
10 gallons is more than enough for a weekend, 25 gallons will last you through a week long cruise for two.
Buy two 5 gallon jerry cans at $10 each, install some padeyes to attach hold down straps, and call it done.

I mentioned it in another thread, I will most likely be able to take a year off of work and go cruising in a couple years. So the extra capacity may come in handy in a place like, say, the bahamas.

I have considered the Gerry Can approach though. I already have a bladder under the v-berth, maybe 10 gallons or so. I could theoretically refill the bladder from gerry cans. Problem is, I have all that space under the cockpit floor that is really not very accessible. I suppose I could cut an access door into the side of the port quarter berth, but it would be a real hassle getting full gerry cans in and out of that space I think...

[toenail]

I'm not too sure what the standards are in the US, but in Australia a company I do some work for make potable water bladders all the time. They are Fabric Solutions

They do mainly larger installs though, but I know they've done smaller water bladders for yachts and other camping expeditions. Plus they have done Australian Military installs for water bladders, and they have to meet a number of requirements there. I have another friend who is into dirt biking and they use smaller potable bladders for their drinking water on longer trips. These are all custom made though, but it all comes down to the material they are made out of. But it still means it should be a problem getting a certified and safe water bladder, it just come down to making it out of the right materials

[mitiempo]

Water bladders are very common - Vetus and Plastimo both make them.