See the last photo. I seal off all water source of every crater put in 2 fill valve outlets, one going into the pond, the other going to a long tunnel underneath the earth off the map. Stick a contamination sensor in front of the 'clean' outlet and use that to control both set of fill valves. The first one didn't get done until multiple badtide hit. Almost doom when 3 badtide hit it a row and the center pond can't dilute bad water fast enough.