vb, a rainwater tank, or cistern, can use several different types of "systems" to keep the water clean enough for potability, or al least for livestock and plantings.
throughout history, people used to line the viaducts and cisterns with lime to inhibit the growth of yucky stuff. my grandfather built one in his house in ireland, then took my dad to dublin to pick up a water closet and bath tub. when they installed it, the whole town showed up to see the indoor
t'was a fiercely rural part of ireland, don't ya know.
today, home systems use everything from uv light to ozone to chlorine systems (but then what's the point if you're making your own pool water?).
in bermuda the roofs are painted white with lime for water collection. apparently, if you drink a lot of limey water, you think it's ok to wear shorts with a suit jacket and knee high dress socks...
oh, and thanks for the tip on the snapple. i'm not big on imitation(?) fruit flavors in tea, but i'll give it a shot. ya never know.