The berky is not just a filter, it purifies also. You can take septic tank water and run it through and it will be safe to drink. If you had to of course! Desperate times might call for desperate measures. Any source of water can be purified and made safe to drink with one. The black filters remove 99.99% of all bacteria and parasites. That's why I say they are a great peace of mind to have. You will always have clean, safe, drinking water if you have one.