Another angle on this water purification issue: Chlorine doesn't
necessarily kill all the bad things you want it to kill, notably giardia
cysts. I've researched the topic a bit and found that iodine is a better
solution to treat water with, This is the "Portable Aqua" method used by
campers but is way to expensive to use for a whole tank full of water
that we pump out of Lake Superior when we don't get it from the tap.

We bought a jar of crystal resublimed iodine (my 100 gram bottle will
likely last me my lifetime) and pour a tablespoon or so (quantity
doesn't matter) into a 24 ounce glass jar. The jar is then filled with
water, shaken up a bit and allowed to sit for an hour. This saturates
the jar of water with iodine.

We then add one ounce of this solution to every gallon we have in our
tank. This ratio supposedly will kill the bad things if it is allowed to
work for a couple hours and if the tank temp gets up to 70, which mine
does because the tank is right next to the motor. If we take the tank
down part way before adding more water, we add only an ounce for each
gallon we put back in so the concentration stays the same.

Some people can taste the iodine at this concentration, but most cannot,
especially if you don't tell them. I RECOMMEND THAT YOU TELL THEM!!!
Some people are very allergic to iodine. Also the iodine crystals are
deadly poison and the saturated water solution isn't going to be
anything you want to mistake for scotch, either. Keep them out of the
reach of others, and label appropriately. (POISON!!!! seems to be
effective). I also filter the water.

If you are using colder water and/or want to have the water ready for
consumption quicker, you need to use a more concentrated solution. You
also may want to check out this ratio for yourself, because I am not a
chemist, pharmacist, medical doctor or anyone else you could trust (or
sue, for that matter) for my expertise in this field.

For What It's Worth,
Capt. Jeff