Don't buy all these so-called water filter, they are scams and expensive. The bacteria will accumulate at the filter.

It's best to buy bottled water in larger 20L container and then pour into water tank every month.

Filter already, bacteria go back upstream? Filters got limited capacity. Just like aircond dust filter, if filter full already then some dust sure break through. Which is why filters must changed/wash regularly.

Problem with bacteria is not its existance, but its concentration.

Watch this: https://youtu.be/LObbHbx_2fY?t=1114

Bacteria stay at the filter because water comes from the dirty pipes. It's only good for washing hands, dishes and shower.
That's why water filter is a waste of money unless you change it every few days.

For drinking, it's better to buy bottled water that is sealed that we can drink for at least 1 week per 20L bottle.