A capful of bleach isn't enough to purify unsafe
water--which is what Roger asking about. Whether you drink it or not, some bacteria can be absorbed through the skin...some can remain alive on dishes etc for quite a long time. However, even when purification isn't necessary, adding ANY bleach to every fill is a bad idea. It isn't enough to kill the critters in the system that make the water smell and taste unpleasant--but are otherwise harmless--but it is enough to eat away at the seals and valves in your water pump. Adding just a capful doesn't cure anything, it only masks the unpleasant smell and taste with the taste and smell of chlorine.Recommission the system according to the directions in the "Fresh Water Maintenance" article in Head Mistress Reference Library (on the right side of the forum homepage) each spring as part of your total boat recommissioning, and and follow the directions in it for filling your time each time...and you shouldn't have to add anything to your tank all season to have water that's as "drinkable" as any that comes out of any faucet on land. Mind you, though, that those directions are ONLY for use where water going into the tank is from a safe municipal water supply...they do NOT purify unsafe water.