Although most people think only in terms of the tank, the plumbing is actually the source of most foul water, because the molds, mildew, fungi and bacteria which cause it thrive in damp dark places, not under water. Many people—and even some boat manufacturers—believe that keeping the tanks empty reduce the problem, but an empty water tank only provides another damp dark home for those “critters.”
There are all kinds of products sold that claim to keep onboard water fresh, but all that’s really necessary is an annual or in especially warm climates, semi-annual recommissioning of the entire system—tank and plumbing. The following recommendations conform to section 10.8 in the A-1 192 code covering electrical, plumbing, and heating of recreational vehicles (which includes boats). The solution is approved and recommended by competent health officials. It may be used in a new system a used one that has not been used for a period of time, or one that may have been contaminated.
1. For a 20 gal tank, prepare a solution using 1 pint (16 oz or 200 ml) of household bleach in a gallon or two of water. Add that to the tank, then fill the tank completely with water.
2. Open all faucets and let the water drain till what's coming out smells strongly of bleach. Do NOT turn of the water pump...it must remain on to keep the system pressurized and the solution in the lines.
3. Allow to stand for at least three hours, but no longer than 24 hours.
4 Drain through every faucet on the boat (and if you haven't done this in a while, it's a good idea to remove any diffusion screens from the faucets, because what's likely to come out will clog them). Fill the tank again with fresh water only, drain again through every faucet on the boat.
5. To remove excess chlorine taste or odor which might remain, prepare a solution of one 1 cup white vinegar to five gallons water and allow this solution to agitate in tank for several days by boat's motion (go sailing).
6. Drain the tank and refill with water.
An annual or semi-annual recommissioning according to the above directions is all that should be necessary to keep your water tasting and smelling as good as anything that comes out of any faucet on land. If you need to improve on that, install a faucet filter on the galley sink.. Just remember that a filter is not a substitute for cleaning out the system, and that filters require regular inspection and cleaning or replacement.
To keep the water system cleaner longer, use your fresh water...keep water flowing through system. The molds, fungi, and bacteria only start to grow in hoses that aren't being used. Before filling the tank each time, always let the dock water run for at least 15 minutes first (wash the boat)...the same critters that like the lines on your boat LOVE the dock supply line and your hose that sit in the warm sun, and you certainly don't want to transfer water that's been sitting in the dock supply line to your boat's system. So let the water run long enough to flush out all the water that's been standing in them so that what goes into your boat is coming straight from the water main...you'll know when because the water will be a lot cooler.
(I've modified these instructions a bit for use in a small tank. The complete instructions for large tanks (50 gal +) are in my book...you'll also find a version of them here if you search for "Fresh Water Maintenance".)
--Peggie
