RO Tank Size

dodgemanJuly 21, 2011

I just had a remote reverse osmosis filter system installed to serve my kitchen sink and my refrigerator.

It's a 4 cartridge system.


1) What is the correct / standard size storage tank?

2) Is 1/4" copper supply to the system adequate?

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Most residential tanks are termed as "three-gallon". This is a bit of a misnomer because typically you will only get around a gallon of down-flow. That's because approximately 60% of the volume contains air pressure which drives the water to dispensers.

Adjustment of that air pressure will provide more or less water but less or more pressure, respectively. Too much air pressure, and the you'll be fighting the membrane (reverse reverse osmosis?) and too little and the tank will be full but not able to provide adequate flow to faucets and especially ice-makers. 7-9 psi is standard.

A 1/4" line, in most cases, will provide enough water. If there is a distance of more than ten feet, increase to 3/8".

I would avoid saddle vale attachments and cut the line and put in a three-way with a ball valve shut off for the source water.
Andy Christensen

    Bookmark   July 21, 2011 at 7:19AM
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andy c is 100% correct.

However, if by saying "remote" you mean your RO system isn't under the sink but is in some location where you have more room, I would strongly recommend a larger tank than "standard". Those "three gallon" tanks andy c describes were made that size in order to fit under sinks. There's no reason to restrict yourself if the tank's location has room for a bigger one. If you have room, I'd use tank 2-4 times that size. You'll get more consistent flow....less instances of fall-off from pressure going down.....less running out of water.

    Bookmark   July 21, 2011 at 9:12AM
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Get the largest tank you can reasonably afford and fit in your available space. We have a 12-gallon, which is perfect (particularly after having lived with the the standard tiny tank previously). We fill 5-gallon coolers of water for the kids' sporting events frequently and have NEVER run out of water.

    Bookmark   July 22, 2011 at 10:43AM
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Thanks for all the replies. I'm still new to water softening/conditioning. After 10 years of putting up with hard city water I just had a softener and RO system installed last week.

The RO system/tank is in the basement - approx. 8' vertical / 8' horizontal from the kitchen. They installed a standard 4.4 gallon storage tank which I believe is rated anywhere from 2 - 3 gallons of water.

I spoke to my water professional and he's going to replace it with a 10 gallon tank. I didn't ask if that was 10 total or 14 with 10 actual capacity. As long as I can get about 5 without significant drop off I'll be happy.

As far as the 1/4" supply line goes, I'm assuming the membrane and filters can only take so much GPM on the inlet side. They did run 3/8" from the tank to the kitchen.

    Bookmark   July 23, 2011 at 8:18AM
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