Plumbing Question - Instant-Hot + Reverse Osmosis faucet

I have done Instant Hot with RO in a few locations over the years - but I am no longer a fan of RO...I think it is overkill for average municipal water.

You can go with a dual handle filter faucet and connect the RO final carbon polish filter output line to both the cold water side of the dual handle faucet and to the hot water tank line without much trouble. You might need a 1/4" T fitting and/or some 3/8" - 1/4" adapters to get things hooked up. Most filter faucets now have 1/4" connections - which matches up nicely with all of the RO tubing.

RO water is somewhat acidic, compared to most tap water, so it is possible it could cause damage to a hot water tank compared to city tap water. I know one brand discouraged using RO water in their hot water setups. I am not sure how much damage will really happen. I used mineral add-on cartridges for a while that added some minerals and increased the PH a little - I didn't notice much of a benefit. Honestly I got tired of the expense and hassle of replacing multiple filters on RO systems - and have had failures and leaks in a few.

I now use a large single stage water filter under our sink - it has a large replaceable twist lock filter that I replace every 2 years. We also have a whole house water filter that helps strip chlroine and other stuff from the city water, so our water is fairly clean and lower in chlorine before it hits our "drinking water" under sink filter. I find the water taste to be better than RO and the PH is a little closer to 7.2 which I prefer.

edit: I also didn't like the lower pressure that the RO system created - this caused problems with our in freezer ice maker and the hot water dispenser. A single filter under our sink doesn't reduce the pressure by much at all so we get better ice production and our hot water tank is happier and spits out water faster...and being in California (read constant drought - this year excluded) RO systems produce a lot of waste water (sometimes 5:1 waste water to filtered water).

gkw4815 said:

Thought I'd pose these question to the TFP community - not pool-related, but at least they're plumbing-related .

When we bought our house, my wife begrudgingly agreed to forgo a kitchen-sink-side "instant-hot" drinking water faucet in favor of a reverse osmosis system/faucet, which I installed. We've been pleased with its performance.

My brother gave my parents an instant-hot system for Christmas last year, but they're reluctant to install it because their hard well water will likely kill it (plus they may be moving before long). They've offered it to me.

I'm exploring whether it would be possible/practical to integrate the instant-hot into my current RO system. I've noticed that some new instant-hot systems (not including mine) actually have faucets with two handles - one for hot water, and one for cold water that's been passed through a single stage filter. I could buy one of these faucets and hook up one side to the existing RO system, one side to the instant-hot output. Should be relatively straightforward.

Alternatively, I could tie the instant-hot system input to one of the following points on the RO filter system:
1) downstream of the RO pressure tank (ie fully RO-filtered water passes through instant hot system)
2) upstream of the RO membrane, downstream of the three pre-filters (GAC, etc)

I've heard that some instant-hot systems can be damaged by pure RO water, so I'm leaning towards Option 2.

FWIW, we get city water and it isn't especially hard. My existing RO system is an iSpring RCC7. The Instant-Hot system my parents have offered me is an InSinkErator HOT150.

Does anyone have experience with combined RO + instant hot systems? Any pitfalls to watch out for? Does tying the instant hot system to the filtration system as described in Option 2 make sense? Or better to keep the two systems fully-separate, except at the faucet?

Click to expand...

Option 2 or separate