I don't know if this is exactly relevant, but ...

I have occasionally created temporary, inexpensive water storage using rolls of 8 mil vapour barrier plastic -- the heavy, semi-clear stuff used in building construction. I would dig a shallow trench about 4 feet wide, 10-12 inches deep, and pile up the dirt around the edge so I would get perhaps 18" of height. This would hold an amazing amount of water (for gardening, usually, but could flush toilets or be boiled to drink). Using eavestrough runoff, it would grow algae pretty quickly; moreso because it had full sun. I put it in a place where I could empty it by gravity feed through a garden hose; I'd aim for shade in a "difficult situation."

Nice thing is, the polyethylene won't contaminate water like vinyl will.

I'd bet I could build the same thing in my basement with 2x6s and good angle brackets. Probably only one board high, though, and never on an upstairs floor. Water in volume is insanely heavy. Some sandbags to reinforce the sides would be wise.