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.Before beginning, turn off hot water heater at the breaker; do not turn it on again until the entire recommissioning is complete.Icemakers should be left running to allow cleaning out of the water feed line; however the first two buckets of ice—the bucket generated during recommissioning and the first bucketful afterward–should be discarded.

1. Prepare a chlorine solution using one gallon of water and 1/4 cup (2 oz) Clorox or Purex household bleach (5% sodium Hypochlorite solution ). With tank empty, pour chlorine solution into tank. Use one gallon of solution for each 5 gallons of tank capacity. (Simpler way to calculate: 1 quart bleach/50 gal water tank capacity)
2. Complete filling of tank with fresh water. Open each faucet and drain cock until air has been released and the entire system is filled. Do not turn off the 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 quart white vinegar to five gallons water and allow this solution to agitate in tank for several days by vehicle motion.
6. Drain tank again through every faucet, and flush the lines again by fill the tank 1/4-1/2 full and again flushing with potable 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 water filter. 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…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. Finally, while the molds, fungi and bacteria in onboard water systems here in the US may not be pleasant, we’re dealing only with aesthetics…water purity isn’t an issue here–or in most developed nations…the water supply has already been purified (unless you’re using well-water).

However, when cruising out of the country, it’s a good idea to know what you’re putting in your tanks…and if you’re in any doubt, boil all water that’s to be drunk or used to wash dishes, and/or treat each tankful to purify. It’s even more important in these areas to let the water run before putting it in the tank, because any harmful bacteria will REALLY proliferate in water hoses left sitting on the dock.

Author “Get Rid of Boat Odors– A Guide to Marine Sanitation Systems & Other Sources of Aggravation and odor”