at the bottom of the tank can get built up with crud. so its always nice to flush it out 2 times a year. if u go out to ur water heater right now and run some water out the bottom u will see the color of it. not the best looking stuff.
i also made a rain barrel last year for the garden. its amazing how fast 55 gallons fills up when it just rains a little. i bought everything and it was less then $20. well worth it. if things went bad for a little while it would be a great way to get water to use. it would still need to be cleaned. bleach, boil or little pill looking things. there a lot of other ways as well to clean water. if it starts to rain the barrel fills up in less then 15-20 mins. i am going to put more in soon to have extra. are garden is below the barrel so it flows out pretty good.
stuck