It is good to store a supply of water. In case of civil unrest, injury, etc where leaving the house may be problematic.

However water is typically used at such a rate that it is difficult to keep enough for a long term situation.

One key is to have a reliable, clean, natural source water that you can count on to remain viable even after a big disaster (a great reason to live in a rural area). Wells, natural springs that are filtered through hills, clear mountain streams etc.

Of course, treat all water before consuming it.