The general rule is storage of one gallon of water per person, per day. But that's just for drinking and cooking, not for dish washing or bathing or flushing toilets. For Houston in the summer, I would double that. Allow extra for pets -- a large dog will drink as much as a person.

If you only store 30 gallons (of course that might change!), that's not enough for toilet flushing. But if you have access to mildly contaminated water (creek, lagoon, golf course lakes, etc), you can use that for flushing toilets. But not for every time someone uses the toilet. Remember the old hippie water-saving rule: "If it's brown, flush it down; if it's yellow, let it mellow."

If you have people who automatically flush (or kids), slip the top end of the chain off the end of arm inside the tank (the other end of the chain is attached to the flapper).

If you plan on filling your bathtub, fill it now and see if your stopper actually holds it for a day or more. Mark the full line with a crayon or tape. Some metal stoppers don't last much longer than a bath takes. Consider replacing with a rubber stopper, if possible.

Also investigate the bathtub Water BOB, a heavy bag that fits inside a bathtub and holds about 100 gallons of water. Useful if you have prior warning, such as a hurricane. Useless for earthquakes.

Sue