DME uses a swimming pool filter designed for sand media. They work very well with activated charcoal granules. I forget the size range. Depending on the chlorine load (usually 1-2 ppm), you can easily get 1000 BBL through one of their units sized for a 10 BBL brewhouse before changing the carbon. Use a chlorine tester to check water purity on a regular basis. I use filtered water for brewing only--not for cleaning. The free chlorine actually helps caustic clean better and at such low concentrations, the residual in rinse water is negligible. Flow rates are good through at least 12 gpm for the ones I'm familiar with, although I imagine they come bigger. 30 gpm would suffice for a 25 BBL brewery, assuming a 30 minute knockout. Good luck & Cheers!