Reverse Osmosis waste water question

Feb 26, 2020 15:35:14

Been doing some research on RO systems today. We purchased a used one a few months back with a plan to use it in our rainwater catchment system to help clean up our drinking water. My thinking was that more filtration etc is better. Now I'm seeing that there is a lot of waste water created in the RO process and as we're feeding into a holding tank I'm obviously keen to keep waste down as much as possible.

Can I just let the RO waste go back into our 2000L storage system? My thinking is that it would get so diluted that it would cease to be a problem. Given that the water in our two 1000L totes gets used for the washing machine, the dishwasher, bathing and pottery, a relatively small portion would actually end up being used for cooking and drinking and therefore shouldn't be an issue.

Any ideas?

Feb 26, 2020 16:03:26

I would use the 'waste water' to flush the toilet and do laundry. Maybe get a smaller tank to hold the water.

I envision a family using 300gallon/day of that 150 is for "RO water for shower, faucet, kitchen" the other 150 gallon of "waste water" can be used for toilet, laundry, pottery/other and seeing as how it is rain water garden/lawn/landscaping too if there is any left over.

Based on the graph above 20% for shower + 19% for faucet + half of the 12% leaks is just about 50%.

I can spend hours in bacteria filled pond water, but if I send it internally via my mouth, I get sick. Similarly if I send those contaminated water droplets into my lungs via a misty shower, I will get sick unlike a bath. For that reason I recommend treating your shower water unlike your toilet/laundry water.

Feb 26, 2020 17:20:29

Hey Andy, I think you'll be fine putting the RO waste water back into your rainwater catchment tank. RO systems generally have a 4:1 efficiency ratio, meaning 4 gallons of water will be used to flush the RO membrane to make 1 gallon of RO filtered water. I don't believe there will be a significant amount of minerals and other contaminants going back into your catchment tank, since the water being filtered is rainwater and doesn't contain undesirable additives like chlorine or sodium fluoride. I believe since the water is pretty clean to begin with, I myself would go ahead and send the waste water back into the tank. Hope this helps!

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