We just bought a home with a well and we are concerned about the drinking water quality. We had the water tested and the hard water has too many dissolved solids according to the EPA (just above 500 TDS) for drinking. After getting quoted $1600 for a Kinetico RO system, I decided to install one myself. This one. Probably a bit of overkill in my opinion.

The problem is that the cold water in my kitchen is plumbed to the hard water (apparently that was a good thing back in '02). I'm told the iron (33 gpg) would ruin the membrane quickly. The basement is finished below the kitchen but I can see 3 water lines running the length of the home (1 hot, 1 hard, 1 soft). I'm trying to decide how to best get the RO water in my kitchen with soft water. I have a few options:

1) Install a bypass in the mechanical room so that the hard water line becomes soft. This would make the entire kitchen on soft water as well as an outdoor spigot (and potentially 2 toilets if those get plumbed with hard water typically?). This would let me put the RO system under the sink.

2) Run a line from the kitchen to the mechanical room and run soft water through it. I have 50ft of 1/2" PEX left over I could use ( the run would be ~40'). With the finished basement the PEX would rest on the sheetrock and run through a bulkhead then between joists. If it just supplies the RO system, I imagine it wouldn't make too much noise. I could install the RO system under sink with this line, or I could install it in the basement and have the RO water run through this line (hoping the pump on the RO system would help with the pressure).

3) Similar to #2, instead of PEX, I could run a more manageable 40' 3/8" PE line and just run the RO water through it from the mechanical room. I'm assuming this line would be easier to run since it is more flexible and thinner.

4) Tear up the basement ceiling and plumb the kitchen with soft water. I'm thinking at least 2 large holes in the textured ceiling (my drywall skills are terrible so I'm kind of dreading this option).

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    Just to make sure... Who tested your water? Make sure the tests are done by someone that doesn't want to sell anything to you. Water filter scams are big business. Installing one yourself is the right choice.
    – JPhi1618
    Jul 16, 2019 at 15:17
  • The person selling the Kinetico RO system tested the water... But I did buy my own TDS meter and confirmed that it was over 500
    – Kreuzade
    Jul 16, 2019 at 15:24
  • In reading your question, it sounds like you have a very good understanding of what needs to happen. So, this really comes down to opinion right? Broad, mostly opinion questions are not a good fit for the site, so do you think there is a specific, technical question you could focus on?
    – JPhi1618
    Jul 16, 2019 at 15:39
  • You're right, it is a matter of opinion. I was hoping to get an opinion of someone who has done it before. My concerns are 1. If the RO system goes in the basement, will there be enough pressure? 2.Will the 1/2 PEX or the 3/8 PE be better suited for this application? 3. Is installing the line unsecured above drywall a bad idea? 4. If i make the whole kitchen soft, will I miss the hard water? There must've been a reason to have it hard in the first place.
    – Kreuzade
    Jul 16, 2019 at 15:50

1 Answer 1


Putting the RO system in the kitchen isn't the best place for it, it's simply the easiest.

Put the RO system in the mechanical room connected to a cold soft water line. Draining in the mechanical room is quieter than draining before the trap on your kitchen dink.

I recommend adding an Aquatec permeate pump (or other brands, that's just the kind I have) to reduce waste water, and less waste water means longer prefilter and RO membrane life. The 100 GPD ones make noise so it's best not to have it under your kitchen sink, but the 50 GPD ones are supposedly silent or at least less loud. Your booster pump will make noise, so a little more shouldn't be too bad.

Install 3/8" PE reverse osmosis line from mechanical room to kitchen sink.

People don't like drinking soft water, so that's why your kitchen sink is hard water. Last year I converted my sister's kitchen sink to soft water, but luckily there wasn't any exterior garden hose spigots on it too. You really don't want to "waste" soft water by using it for outdoor garden hoses, but on the other hand it will leave less water spots on your car if you hand wash it. Since you'll have RO drinking water at your kitchen sink, I would switch the sink to soft water as a separate project at a later date.

You can leave the 3/8" PE supported by drywall, but it'll probably bounce around and make noise in the joist bay/cavity. That's probably not code compliant, but I'm not a plumber so others can speak to that potential violation better than me.

Personally I'd leave it supported just by drywall for now, and go back and support it later when you open the drywall up to add the 1/2" PEX for the kitchen sink soft water line. I'd assume that you definitely would need to support the 1/2" PEX, and not leave that supported by drywall. Leaving the hard water line available at the sink would make future owners happy in case they delete the RO system and want hard water at the kitchen sink again.

The pressure loss over 40' with 3/8" PE is not going to be a problem as long as there are no bottle necks. Three potential bottle necks are to make sure that your storage tank has a 3/8" line/connection, and also that your post filter has a 3/8" line/connection, and your faucet has a 3/8" line/connection. Sometimes these are only 1/4".

If you're buying a new system, I'd customize it more. I can't tell how many gallons that tank is, but a bigger tank is usually better if you have the room. Those small tanks only have about 1-2 gallons of capacity.

With a larger tank, booster pump, and with a permeate pump, you can increase the pressure of the air blatter from 8psi to 15-20psi to make sure your RO water pressure doesn't drop as much. Higher air bladder pressures decrease the amount of tank water capacity slightly, so I wouldn't do that on a system with a small 3 gallon tank. Higher air bladder pressures usually increase waste water as well, but not if you have a permeate pump.

I actually have my booster pump before my prefilters, but I'm on city water. It's recommended to prefilter the water before the booster pump, but I'm more worried about the lack of pump feed volume by having 3 prefilters before it. As those filters get clogged, it reduces the inlet flow and can cause pump impeller cavitation. My city water feed pressure is 60 psi, and my pump boosts the pressure to 100 psi before it enters the RO membrane for higher efficiency. It's probably fine after the filters though and I'm just being over cautious. If you're on well water, you definitely need some kind of filter before your booster pump, so just watch (listen) for pump cavitation as your filters get dirty.

Having a booster pump increase the water pressure to 100psi before the 3 prefilters can cause filter channeling, so I buy solid charcoal filters instead of granulated charcoal to mitigate that risk.

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    Wow, thanks for the write up. So the booster doesn't increase tank pressure? a permeate pump does? Do both increase efficiency? I'm pretty sure the fittings are 1/4" on the system, I had planned on using an adapter to switch to 3/8" for the main run. Should I find a system that uses 3/8" instead? (tank is 4 gal)
    – Kreuzade
    Jul 17, 2019 at 16:27
  • @Kreuzade A permeate pump uses the waste water's pressure that is normally wasted to help pressurize the good water. The effect is that it removes the back pressure load from the RO membrane. Without one, the membrane has to fight the tank pressure to filter water, which lowers the efficiency. A permeate pump can't increase pressure above the membrane pressure though. A booster pump increases the pressure going into the RO membrane, which will allow higher efficiency than if it was at lower pressure. Basically a system with both allows you to raise tank pressure without decreasing efficiency.
    – Dotes
    Jul 17, 2019 at 22:24
  • @Kreuzade Yeah, I'd probably look for a system with all 3/8" connections starting after the RO membrane housing. (I don't think a residential RO membrane housing with a 3/8" output exists.) So that's basically just the tank, post filter, and faucet. Everything else is fine being 1/4".
    – Dotes
    Jul 17, 2019 at 22:34

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