Here is the process we use
From PEGGIE HALL’S LIBRARY OF CLASSICS
Fresh Water Maintenance
Most fresh water system problems - foul odour or taste - don’t originate in the tank, but in the plumbing
, which is an ideal environment
for molds, fungi and bacteria that thrive in damp dark places. Here’s the recommended method for recommissioning fresh water systems; this should be done at least annually. l Fill the water tank with a solution of 3/4 dl. of household bleach per 10 litre tank capacity. l Turn on every faucet on the boat (including a deck
wash if you have one). l Allow the water to run until what’s coming out smells strongly of bleach.
l Turn off the faucets, but leave system pressurised so the solution remains in the lines.
l Let stand overnight - at least hours - but NO LONGER THAN 24 HOURS.
l 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, ‘coz what’s likely to come out will clog them).
l Fill the tank again with fresh water only l Drain again through every faucet on the boat, repeating till the water runs clean and smells and tastes clean.
Remember: cleaning out the tank addresses only the least of the problem ... most of the problem occurs in the lines, so it’s very important to leave the system pressurised while the bleach solution is in the tank to keep the solution in the lines too.
People have expressed concern about using this method to recommission aluminium tanks. While bleach (chlorine) IS corrosive, the effect of an annual or semi-annual "shock treatment" is negligible compared to the cumulative effect of holding chlorinated city water in the tank for years. Nevertheless, it’s a good idea to mix the total amount of bleach in a few gallons of water before putting it into either a stainless or aluminium tank.
People have also expressed concern about the possible damage by the rubber and neoprene parts
in a water pump. Again, the cumulative effect of putting chlorinated water through the pump is more damaging than an occasional "shock treatment". Occasionally, water pumps have been known to fail after recommissioning, but they’ve always been older pumps; recommissioning only "pushed ‘em over the edge" a month or so sooner than they’d have failed anyway - which I consider preferable to finding yourself without water during the second week
of a 3 week cruise
To keep the water system cleaner longer; USE your fresh water ... keep water flowing through the 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 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.