My house has well water and a reverse osmosis system for drinking water. The water for the RO system is plumbed through a prefilter, an automatic shutoff valve, the RO membrane, through the other side of the automatic shutoff valve, then tees off to a pressure tank and to a postfilter, then from the postfilter out to the drinking water faucet. It's all 1/4" PEX with push fittings. The filters and tank are located directly below the sink close to the crawl space floor; it's about 10' from the faucet to the crawl space floor.

I would like water to exit the drinking water faucet faster. What's my best course of action?

  1. Move the pressure tank to be after the postfilter instead of before?
  2. Add another pressure tank after the postfilter?
  3. Use larger diameter plumbing and faucet?
  4. Something else?

One thought that comes to mind about option #1 is that the automatic shutoff valve would then turn on the water supply immediately every time the faucet is turned on (assuming sufficient pressure drop across the postfilter), not just when the tank pressure is low. I don't know if that would be bad for the lifetime of that valve.

At some point I'd also like to get more filtered water to come out before it peters out. That obviously requires a larger pressure tank. I guess I'm mentioning that only to say option #2 doesn't sound like a waste of money to me: I could just buy a large pressure tank now instead of later and put it there. But I'd also be fine delaying that expense if I can get better flow rates for cheap.

And my faucet is leaking so I'll probably be replacing it soon. (It's a non air gap version, so I don't think the leak is serviceable) So #3 doesn't sound like a waste of money to me, either, in the sense that I'll be getting a new faucet anyway. I'm just not sure if my plumbing dimensions are more restrictive than my postfilter.

P.S. I'm asking about initially higher flow rates. I'm not interested in increasing my filtering capacity at this time.

  • 1
    Increase the capacity of the slowest part - we had to meet a flow rate and ended up with 4 RO in series with 4 sets in parallel so 16 working... Then an extra set for rotating in-service units...
    – Solar Mike
    Jun 12, 2021 at 22:51

1 Answer 1


Your problem is not so much the low flow rate but the limited amount of storage you have. Quite a few years back I set up a 50 gallon reservoir tank and booster that fed the existing pressure tank.

This was basically the same system that you have but I added the tank and booster pump. The booster pump after the reservoir.

The Ro system was changed from the pressure switch activation to a level sensor activation and the existing pressure switch was changed to run the booster pump.

I thought the 50 gallon reservoir tank was a bit excessive I thought a 15-20 gallon tank would be more than enough.

The owner was delighted with the results he said he never ran out of good water even when the system was flushing.

By increasing the storage beyond the pressure tank the system produced water until the tank was full. We did not try to just increase the pressure tank because it was more expensive than the reservoir tank and pump the RO system required.

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