Preserving water

[Modem]

MA>> I have a mobile home that uses water off of a 40 gallon storage tank.  Thi
MA>> refilled about once every 2-3 mos.  Being conscientious of potential micro
MA>> development during the storage period, I'd like to know how much chlorine 
MA>> need to add to the tank to keep it 'sterile'.
MA>> 
MA>> Any suggestions?
MA>> 
MA>> Thanks.
MA>> 
MA>> May
My old Boy Scout Handbook recomends adding one quarter teaspoon (16
drops) of liquid chlorine bleach (5.25% sodium hypochloride normally but
may be 4 to 6%) to each gallon of water and letting sit for 30 min
before drinking.