As mentioned the water in the WD unit does NOT recirculate. It's a one-way trip through the machine. It also doesn't have a heater so water should be relatively tempered. That said, I did set mine up to be recirculating. I use a 5gallon or so Phototherm tempering bath and it's pump to feed the WD module. The drain from the WD drains back to the phototherm model 14 tempering bath. yes, not as good as fresh water, so I change it frequently. But, it's the only way I can use it in my current darkroom which doens't have running water yet.