RO/DI Units

akcnmom65 · Jan 21, 2016

Hello Everyone,

I thinking about buying a RO/DI unit for my tank but I've heard they waste about four gallons of water to every one of RO/DI water, is that true? Can you use the waste water for drinking, watering the garden, washing the car, etc. I will take any advice.

moulton1853 · Jan 21, 2016

I don't think I would drink it but you could use it for other things like washing or watering the garden.

Busa1340 · Jan 21, 2016

I wouldn't drink it.. But than again it's still just as dirty as your tap water maybe even a tad cleaner. Depending on the unit you get the waste to good water ratio will vary a little. I'm still trying to figure out how to store my waste water. Here in Cape Coral FL there's water guidelines so I don't want to waste all that water.

redfishbluefish · Jan 21, 2016

The answer is yes, yes, yes and even yes to etc. I use mine for laundry and, in the summer, watering. I have a 55 gallon drum to collect it. Lets assume your TDS is 200 and, as you stated, you produce 4 gallons of waste for every 1 gallon of good water (I do a little better then this).....(and all the TDS goes to this collection container (you do have the last bit going to DI). The theoretical TDS of this collected water will be 225 TDS.

The one caveat is if my water was extremely high (I beleive there is a "recommended" maximum number, but nothing in water quality standards of an actual limit), I'd be reluctant to drink it. But note, if the raw water was this high, I'd be reluctant to drink it right from the tap anyway.

akcnmom65 · Jan 21, 2016

Thanks for all that great advice. Can I turn off my RO/DI unit off when I have no need for water?

Busa1340 · Jan 21, 2016

If you have a dedicated sink just turn the water off.. If not unhook the unit and store it under sink ect. It is good to flush the system in between usage to get that settled water pushed threw it. Enjoy.

jsker · Jan 21, 2016

akcnmom65 said:
Thanks for all that great advice. Can I turn off my RO/DI unit off when I have no need for water?

Yes, it is recommend not to leave the RO/DI on when not filtering. You can find all of the connectors at the big box home improvement stores or on line. I have mine mounted above the washer so that my waist is not wasted.

rdela55 · Jan 21, 2016

You can drink the waste water, it's just the same as the water you are putting in the filter. You can do the same things with the waste water as you can do with the regular tap.

akcnmom65 · Jan 21, 2016

Thanks, everyone for that great info.

AZDesertRat · Jan 21, 2016

The TDS of the brine or waste is 20-25% higher than the tap water TDS going in. This applies to any RO or RO/DI system operating at the manufacturers recommended 3:1 to 4:1 waste ratio. The reason is the TDS removed from that one treated gallon is concentrated in the 3-4 gallons of waste it takes to keep the membrane flushed and operable.
If the water was potable to begin with I suppose you could drink the waste but I don't suggest it. Yes it has been through a sediment and carbon block filter but those only remove the large particles and the residual chlorine disinfectant but is not cleaner than the tap water since it has all the contaminants from the treated water in it.
RO membranes only run when you make water and can be shut off when not needed. I always leave my systems under pressure to reduce the possibility of something entering and contaminating it. If I make 100 gallons of RO I waste 400 gallons so the total usage is 500 gallons or about $2.50 worth of water. Really it does not go to waste, it goes into the sanitary sewer to be recycled over and over.

Busa1340 · Jan 21, 2016

AZDesertRat said:
The TDS of the brine or waste is 20-25% higher than the tap water TDS going in. This applies to any RO or RO/DI system operating at the manufacturers recommended 3:1 to 4:1 waste ratio. The reason is the TDS removed from that one treated gallon is concentrated in the 3-4 gallons of waste it takes to keep the membrane flushed and operable.
If the water was potable to begin with I suppose you could drink the waste but I don't suggest it. Yes it has been through a sediment and carbon block filter but those only remove the large particles and the residual chlorine disinfectant but is not cleaner than the tap water since it has all the contaminants from the treated water in it.
RO membranes only run when you make water and can be shut off when not needed. I always leave my systems under pressure to reduce the possibility of something entering and contaminating it. If I make 100 gallons of RO I waste 400 gallons so the total usage is 500 gallons or about $2.50 worth of water. Really it does not go to waste, it goes into the sanitary sewer to be recycled over and over.

500 gallons only 2.50$???wow that sounds crazy! My water must be higher here in south Florida cause I haven't even hooked up my RO unit and my water bill seems high lol!

AZDesertRat · Jan 21, 2016

That's about average across the US. $5.00 per thousand gallons including water and sewer rates combined. Here in AZ its a little higher in summer months and lower in winter months and about spot on in the shoulder months. What makes ours deceiving is they lump library fees, fire dept fees, environmental assessment and a bunch of other stuff in the bills so you have to go online and weed out everything to see what you actually pay.
Nationwide though a good reef quality RO/DI makes a gallon of RO/DI water for 5 cents on average. That nickle includes not only water and sewer charges but also replacement sediment and carbon block filters and DI cartridges. You can't beat the cost or having ultimate control of your water quality.

Busa1340 · Jan 21, 2016

Well dam I must be taking long showers lol great info thanks @AZDesertRat

AZDesertRat · Jan 21, 2016

Check your utilities website.
I have a 15,000 gallon in ground pool, grass lawn front and back, evaporative cooler in the mild months, a wife who is retired and home all day watching grandkids and lots of garden and landscaping in the AZ Desert and my water and sewer portion of the bill is around $28 in winter and $50 in summer.

Busa1340 · Jan 21, 2016

Might have to check that lol we pay 82! But utilities in my town are high.

Busa1340 · Jan 21, 2016

Just found out we have a 50$ minimum even if you use nothing lol yay!

AZDesertRat · Jan 21, 2016

Check the usage rates. The $50 stays regardless of the usage so can't be counted against a RO units consumption.

Busa1340 · Jan 21, 2016

Yea I'm not really worried about it.

SaltMan · Jan 21, 2016

Try adding a second membrane, you can double your production at half the waste. You have to have 65 psi or better or have a booster pump for it to work efficiency. Look up BRS 150 GPS water saving upgrade.

AZDesertRat · Jan 21, 2016

BRS is out in left field on those bogus claims.
Dual membranes are not water savers, on fact it is the opposite. You are sending the concentrated waste from one membrane so it is critical you keep the waste ratio up if you expect the membranes to last as they should. If you don't mind the extra cost of replacing membranes prematurely this would work for awhile I suppose. They haven't been in business long enough to know better in my opinion. If it really was that easy don't you think all the vendors that have been in business for 20-30 years and have excellent reputation would have been doing this decades ago? It's just not the case.
Dual membranes increase gpd but reduce the rejection rate slightly since the TDS surrounding the membranes is higher. It does not or should not reduce the waste unless you budget for more frequent replacements.