I posted a question about water filtration a few days ago, and it's become clear that I'll probably need an RO system to reduce high TDS/alkalinity/ph in my water. I've started researching some options, and have come across a few plumbing questions ... figured I'd start a new thread to keep things organized.

I'm looking at homeowner-level systems to keep costs reasonable, like iSpring (#RCC7AK) or Watts ... each around $200 with added calcite/alkaline stage to remineralize water. These systems come with 1/4" tubing. The RO has an accumulator tank that I can pressurize to, say, 40 PSI (when full). Water goes from the tank through two more filters (carbon and calcite), and exits through a 1/4" tube. In my last plumbing setup, I ran 1/2" tube to the 3/8" supply at the machine, and as a result have a bunch of fittings -- regulators, gauges, etc. -- for 1/2". My question is,

- Does it make sense to couple the RO's 1/4" line to a 1/2" line downstream, for which I could reuse my regulator/gauge/tees? Or does it make more sense to just stick with 1/4", and get a new 1/4" regulator/gauge downstream (Chris Coffee's JG one would run about $80)? I like the first option (I get to reuse my solid Sharkbite fittings), but somehow expanding from 1/4" to 1/2" feels ... wrong.

Before going too far into this, I suggest you contact the RV Water Filter Store (http://www.RVWaterFilterStore.com). While you don't have your coffee machine an RV (I'm guessing), we did. If I recall the man's name is Richard and we found him very helpful when setting up our whole-RV RO system. What we learned from him applied totally to installing an RO system in our new house. We have no interest in this business...just satisfied customers. Turning to your question, I can think of no good reason to buy a bunch of new 1/4" stuff if you already have 1/2" infrastructure in place.

Our installation is a standard under-sink type RO unit, except it is installed in our mechanical room. From there, we ran 3/8" flex tubing to our winery, kitchen (refrigerator & coffee station), reducing to 1/4" to make the connections to the appliances/spigots.

A few suggestions. Buy a system that uses standard 10" filters, not proprietary ones. Replacement filters are less expensive and available in more greater variety. Also, if you need more capacity, it is really easy to add a second membrane, which we did on our motorhome. If you find you want more pressure, you can buy a hydraulic (passive) pump. We added one to our motorhome system and to our household system. It uses the waste water to increase the pressure to 100 psi (you can add a little plastic regulator if you want to cut this back a bit). At the higher pressure, the filters last longer, the water comes out much faster, and the purity is improved (these systems are designed to be optimum at 100 psi, I think).

Good luck!

Good points, thanks. The iSpring does use standard 10" filters, and requires at least 45 PSI line pressure -- which I should have (though I'll have to double-check).

My primary concern is about flow rate and pressure from the tank. I know I can pressurize the tank to a set PSI, and that tank PSI drops as the tank gets emptier. But I don't know how much the tank pressure drops after pulling, for example, 10 oz (HX cooling flush, coffee, clean). Though I suppose that with a 3 gallon tank at 40 PSI, and a regulator set to 30 PSI downstream, it's unlikely that even a few sequential shots would cause pressure to drop below 30 PSI.

My primary concern is about flow rate and pressure from the tank. I know I can pressurize the tank to a set PSI, and that tank PSI drops as the tank gets emptier. But I don't know how much the tank pressure drops after pulling, for example, 10 oz (HX cooling flush, coffee, clean). Though I suppose that with a 3 gallon tank at 40 PSI, and a regulator set to 30 PSI downstream, it's unlikely that even a few sequential shots would cause pressure to drop below 30 PSI.

I think that the fatter pipe can only improve your flow rate, not hinder it. Also, the typical RO tank holds a gallon or three. So, a few ounces is not going to make much difference. In our RO system, I routinely take a gallon out for our winery and although the pressure does drop, it is not too noticeable. Besides, if you find the pressure is too low for your liking, you can always add that passive pump...it sort of operates like a turbocharger in a car engine.

As for the tank pressure, that's one thing that I learned about where you must be careful. In a standard well pump, one pressurises the tank bladder to somewhere around the operating pressure of the switch as I recall. Not so with the RO tank, for which 7 psi is the normal pressure. Many suppliers and plumbers do not know this and they pump them up way too high. This makes the RO unit take a very long time to recover. The RO unit wants to see no pressure at its output, as it likes up to 100 psi pressure differential between the input water and the output. Eventually, when the RO system achieves balance, the pressure in the tank will be the same as the pressure of the feed water. As you use water, it gradually drops from that (typically 65 psi) to zero when all the RO water is delivered. Or, with the additional passive pump, it starts at 100 psi and gradually drops. BTW, another benefit of the pump is quicker recovery.