The instructions on my gravity filter say you should "backwash"–reverse the flow–whenever the filtration rate slows. My question: What do you do with the water that is "backwashed" into the "dirty" bag? Discard the water or re-filter?
Submitted by - Anne - Oxnard, CA
Gravity filters are a great solution for big groups looking to filter water in camp. (If you’re not sure how they work, check out our slideshow.)
But, I’d never thought about what to do with the dirty water before now. In most cases, I’d say just pitch it and start over with fresh stuff. But if you’re in an environment where water is hard to come by, there’s no reason you couldn’t be thrifty and re-filter it. I confirmed this with Erik Flink the filter guru at MSR. He says, “Re-filtering will just remove all the gunk you just backflushed out. However, the gunk obviously will reclog the filter cartridge so you may get slower flow rates. Keep backflushing occasionally to maintain flow.”