[BrewBama]

I’ve been running a gallon for use in my coffee pot and ice tea maker and keeping it in a gallon jug overnight. I don’t think I would hold it in that jug long term though.

[mabrungard]

Thanks Martin. Would you have any concerns leaving carbon filtered RO water sit in a jug or tank for an extended period of time? It's no longer chlorinated so I'm always wondering how long is too long. I realize the sanitization of the storage vessel matters here too but just wondering what your thoughts are on that.

The building blocks of life are carbon, nitrogen, and phosphorus. There is very little of those components in RO water. Therefore, there’s little opportunity to grow anything in that water. I wouldn’t worry about pathogens in that water.

[Buckeye Hydro]

By "concentrate" I think you mean the "water you want to filter", correct?

Concentrate is commonly referred to as "waste water"
The water coming to an RO System is called "feedwater"
The purified RO water is called "permeate"

You mention you have very hard water.  That said, you'll want MORE concentrate flow so that you don't plug your membrane with scale.  There are no "magic membranes" out there that avoid the issue of scaling.  But if you have soft, or softened water, you can reduce the concentrate flow to around a 2:1 and still get a reasonable life span out of a very low flow residential RO membrane.

So, if I did go with R/O that should be connected downstream from the output of the water softener?

Correct - feed the softened water to the RO.

Russ

[Buckeye Hydro]

There's always been a lot of confusion surrounding the issue of "waste water."  The thought that, as a blanket statement, "less waste water is better" couldn't be further from the truth.

Additionally, all the claims regarding the "wastewater ratio" go out the window once you add a pressurized storage tank to the system.  As a pressure tank fills it exerts more and more back pressure.  The higher the back pressure, the less pressure the membrane has to work with (called "NDP" or net driving pressure), and the more concentrate ("waste water") is produced.

So, if you want the fastest RO water production, the most pure RO water possible, and less concentrate -> avoid use of a pressure tank.

Is there a workaround?  Yes!  That's a high pressure auto shut off valve and a permeate pump.  But those two items are nearly unknown in the residential RO market.  We stock them both.

Russ Romme

[ynotbrusum]

There's always been a lot of confusion surrounding the issue of "waste water."  The thought that, as a blanket statement, "less waste water is better" couldn't be further from the truth.

Additionally, all the claims regarding the "wastewater ratio" go out the window once you add a pressurized storage tank to the system.  As a pressure tank fills it exerts more and more back pressure.  The higher the back pressure, the less pressure the membrane has to work with (called "NDP" or net driving pressure), and the more concentrate ("waste water") is produced.

So, if you want the fastest RO water production, the most pure RO water possible, and less concentrate -> avoid use of a pressure tank.

Is there a workaround?  Yes!  That's a high pressure auto shut off valve and a permeate pump.  But those two items are nearly unknown in the residential RO market.  We stock them both.

Russ Romme

That is the conclusion I reached based on my own anecdotal reference of my system.  When the open collection tank in my garage is filling, the RO system output is much higher than when I shut off the collection tank valve that I have feeding through the loose tank cover and the basement pressure tank fills (I hear a periodic loud croaking sound due to the undersink drain connection.)

[Buckeye Hydro]

Yep - when filling an UNpressurized tank (aka an atmospheric tank) the Net Driving Pressure (feedwater pressure minus any backpressure) is equal to your feedwater pressure.

When you're outputting to a pressurized storage tank your Net Driving Pressure is equal to your feedwater pressure minus back pressure from the tank.  In the most common configuration, that would look something like this when the tank is almost full, assuming you have 60 psi feedwater pressure:
 60 PSI feedwater pressure
-40 PSI backpressure
 20 PSI Net Driving Pressure.

The best residential scale membranes on the market are produced by Filmtec.  They are factory spec'ed at 50 PSI.  So you can imagine how poorly they will perform with an NDP of 20 psi!

Low NDP results in low rejection (the purified water is not as clean); and low recovery (much more of the feedwater goes down the drain rather than through the membrane).

Russ