Err....some thoughts on all of that:

Many people have no idea about their hot water system. Is it gas or electric? Is it actually a tank or is it tankless and using a heat exchanger? GO LOOK NOW.

When if ever have you drained it? Most people haven't. GO LOOK NOW and try draining a little when not in operation. Many have lots of corrosion from rust and sediment from soldering agents in piping plus grit. Better to know now, then when you are thinking, "Oh I'm covered on water supply."

Don't drink water from toilet tanks. They most often have very high staph content and you may just have dosed your family with contaminated water. Not wise.

Filling up your bath tub means not being able to have a dedicated place to clean from. It's true that short term you could rapidly fill it with water for flushing. I would never drink water from a tub without a lot of treatment. The dirtiest places in your home are places with sinks. It's a guaranteed way to vastly introduce bacteria into your body.

It's possible to purchase a water bob and therefore create a source of water to drink short-term.

Long term you can't flush or drain the tub since sewer systems may not be able to cope or operate. See Hurricane Sandy especially high rise apartments.

I encourage you to research everything I say for veracity.

Many of these issues are specifically and carefully dealt with 600+ postings in:
Thread: Last minute tips for parents when the SHTF