Operation Olive Water – Saving Reverse Osmosis Waste Water

A few years back I was heavy into reef fish tanks. Fast forward 7 years, 1 kid later and there is simply no time for salt water tanks anymore.

I had an old 5 stage RO/DI system I used for the fish tank which has since been converted to provide drinking water and ice in the kitchen.

The thing that irks me about RO systems is the amount of waste water they produce. I’ve read that it’s anywhere from 5-10 gallons of waste water per gallon of fresh water produced. That’s a huge waste and I have a huge lawn and garden that could use all this “waste” water. The higher the pressure in an RO system, the less water is rejected so I purchased a permeate pump. I already had about 70PSI coming from the tap but the permeate pump up’d the pressure to close to 90PSI. After doing some tests, for every 1 gallon of pure water, 6 gallons is rejected.

Potential problem number 1 was getting the water from the RO system to a storage tank to the backyard. The waste water is rejected through 1/4″ plastic tubing, and usually goes straight to the under sink drain. I figured I could put a small hole in the cabinet and floor under the sink and run the tubing under the crawlspace through a ventilation grate and out of the foundation to the back of the house. I did some head calculations to determine how much pressure would be required to push this water over 100ft away with about a 5 foot elevation change. Turns out it would only take about 8PSI to push the water to the storage tanks, sweet!

Next I purchased a couple of used Olive Oil 55 gallon drums off of craigslist and built a stand out of some spare 2×4″ and 3/4″ plywood I had.

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I paid $25 for 2 of drums. I connected the 2 tanks together with some 3/4″ PVC, a couple ball valves, and a union between the two. I used a few poly bulkhead fittings from Amazon for about $6 a piece.

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A little trick to get the bulkheads installed: Use a piece of string/rope, this blog has some great photo’s and instructions on how to do it:

Install bulkhead fitting in drum

For reference the RO/DI system is from Air, Water & Ice

http://airwaterice.com/reefkeepers-rodi/mighty-mite-50-gpd-with-di-added.html

I changed out the membrane to a 75GPD, removed the DI, added a 5 gal under sink storage tank, and added a couple more carbon filters.

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