You need to empty your vat into the main tank.
Alina & Vina can do it in auto-mode if you ask them., or you can do it yourself.
Containers --> To recolt rain water (or ask yourself/Lacy to fill it with water from the well)
Vats --> to Filter rain water
main tank --> Empty your vats inside the main tank to store water (or ask Alina/Vina to auto-do it)
You can keep track of these 3 in the stat menu (in your phone).
If you're still in emergency, you can ask Aidra to help you in the morning (but you will consume fuel).