When the power goes down for a longer time, the drinking water will get contaminated very fast. In that case, you need to be prepared. Ofc you need a water filter and purification tablets, but you also need lots of water by the hand.
A very handy tip I could give you: when the power goes down, make sure to fill up every bottle or can you have with drinking water, and do it fast, before the drinking water gets contaminated.
Fill up your bath immediately with water (this is soooo important). And you will have lots of water with you all the time.
Another thing you could do is buy some jerrycans (specific for water) and use them when you notice that the power goes down.
Water is life saving, always be prepared!