How much water does a ro/di unit discard?

[glb]

I've been reading up on these but wonder about the waste water. I pay for city water so I wanted to know the ratio of ro/di water to waste water produced. I have a nano now so buying ro water is cheap, but I want to upgrade to a bigger tank in the future.

 

[patrickreef]

The RO/DI units will list what the ratio is of waste water to RO/DI water produced. The unit I have is about 4 gals of waste water to 1 gallon of RO water

 

[pam0630]

lots......i fill empty buckets with that wasted water..water your plants...fill alittle pool for my ducks.....it does waste alot of water...........i can fill an empty bucket with the wasted water much much quicker than i can with the R/O water/ always try and find things to do with that wasted water//////////

 

[jeremyblu]

Usually it is 2.5 to 4 gallons per 1 gal good so fill some barrels lol

 

[dwilliams87]

If you are only getting 2.5 gallons waste to 1 gallon product, you may want to check the quality of your product water. You either have extremely great city water or your RO is not performing optimally.Typically you want at least a 90% rejection rate.

 

[AZDesertRat]

The standard waste ratio is 4:1. If you are using softened water and have lower than normal TDS (the national average is around 250) then you may be able to reduce that to 3:1 or in rare cases 2:1.

Really though its not as expensive and you would think since it only wastes while you are making water. Say you make 100 gallons a month you waste 400 gallons. Water around here costs about $3.00 a thousand gallons and the sewer charge is similar so say that 500 gallons cost me ($3+$3/2 = $3.00) $3.00. 100/$3 = about 3 cents a treated gallon. Add in the cost of replacement sediment and carbon block filters every 6 months or so and DI resin and its more like a nickel or a little more per treated gallon.

The brine or waste isn't really wasted, its not gone, it gets sent to the sanitary sewer, treated and recharged back in the ground or used to water parks, golf courses or to fill a stream or lake. It gets recycled over and over.

 

[glb]

Thanks everyone! I'm not sure how much our city water costs. I'll check it out. I think ro water at the lfs is 50 cents a gallon.

 

[AZDesertRat]

With a small system purchasing water isn't a big deal but when you start needing more water the cost and the trouble of lugging jugs around combined with your time and gas adds up quickly. Doesn't take long to pay for a good RO/DI system at around $130. Then having ultimate control over you water quality has to count for something too, you don't have to depend on anyone else and their filter maintanance or lack thereof.

 

[redfishbluefish]

You can reduce your waste water ratio by using a dual membrane RO unit.

 

[Raptor72]

My waste water goes into an outside rain barrel which then waters my plants around the house.

 

[Ron Reefman]

I have a big, BIG RO system used by coffee shops which makes 18g an hour. It runs at 120psi and has about a 6:1 reject ratio. So I set up a 200g cistern from a well water system and store the reject water in it. I use it to do the laundry. My wife loves it because I now do the laundry and our water bill went down about $15 a month! I kept my old RO/DI system in place above the new one in case it ever breaks down.

 

[AZDesertRat]

You cannot reduce the waste by uing dual membranes, if someone told you that they are uninformed. You are taking the concentrated waste from the first membrane and running it through the second so it is even more important to keep the waste ratio up if you want decent membrane life. there are a few newer vendors promoting this but talk to the RO manufacturers and vendors who have been around for decades or klonger an not one will tell you this. They have a reputation to protect so wouldn't make a statement like that or sell you something that will not work long term. Sure you can do it but the cost of ownership will go up accordingly in more frequent membrane replacements and shorter DI life. Dual membrane increase production but do not save water.