Just boil it, it can't go *that* bad if it's trapped in air tight bottles. The worse thing is it will get some weird growth which can be boiled away. Boiling is your friend
If you are going to spend the money, build a solar still.When I was 18 I took an Outward Bounds course in the mountains of Colorado. We used iodine in liquid form (thats probably the active ingredient in the tabs you are talking about. It takes awhile to get used to the tasted of iodized wated, but it drinks just fine. We always got our water from moving sources of water, I don't know how it would clean up stagnant water. Get a jug of bleach and a camp stove for boiling your water....$40 and you'll be covered...unless you want top of the line camp stoves. If you are OK with a larger coleman model to keep at home you'll be fine.
Just my 2 cents.
I bought a water purifier pump, PUR, and it claims to make the most undrinkable water drinkable. I haven't used it yet so I can't recommend it, but I like the idea.