I would buy a better one......is called a "water bed".....would hold around 200 gallons and all that you would have to do is to put a couple of spoonfull of clorox before filling it.
If you want you can change the water every couple of years, good for drinking, toilet or whatever.
If you are referring to an actual waterbed (a bed matress of water), I believe they recommend you NOT use them for water storage because the insides of the bladders contain an anti-algae or anti-microbial compound or some other tasty chemical.