I'm considering getting a "comfort pump" which will pump water from the hot line to the cold line under a sink so that there is no waiting for hot water, as well as saving the wasted water.
My concern is that the hot water is getting pushed back into the cold line and that will get fed into the reverse osmosis filter, and that the filtered drinking water will no longer be as good. I've seen numerous articles that state that contaminants from the hot water heater are not good to drink.
Then again, it might be just such a small amount of this water that gets into the RO filter, and the RO filter might do such a good job of eliminating contaminants that this problem won't be an issue.
I'm considering these 2 models of "comfort pumps":
- Watts 500800 Premier Hot Water Recirculation Pump, Blue
- Grundfos 595916 1/25 Horsepower Comfort Series Recirculator Pump
This question is related:
Are hot water returns worth putting in?
I got this response from Watts:
The small amount of water from the hot water heater that may make it
to the RO system will not matter. The RO does not allow water in
constantly, only when pressure has been bled off the storage tank, as
when the faucet has been opened, and if it does, the reverse osmosis
system will reject the contaminants that may be present, mainly
calcium and/or magnesium deposits, which could build up the water
heater. The reverse osmosis system should not be a determining factor
for installing a hot water recirculting pump, as it will have no
effect.
I got this from the Hot Water Lobster. I'm skeptical of the claim that the powered pumps only last 18-24 months. I'm also skeptical of recirculating the water during the middle of the night.
On the other hand, when it's sunny where I live, I see no disadvantage circulating the hot water all day long, as my hot water tank would get unreasonably hot such that I had to add a thermostatic mixing valve.
The Hot Water Lobster Instant Hot Water Valve is thermostatically
controlled and opens only when the hot water temperature at the HWL
drops below the adjustable temperature setting (allowing thermal
convection to slowly move the water through the system until it
reaches your set temperature). With the Hot Water Lobster Instant Hot
Water Valve, you should get hot water within 4-8 seconds at the faucet
where the Hot Water Lobster Valve is installed. Powered pumps
circulate the water at a faster rate than the thermal convection
generated within your hot water tank. However, the speed the water
circulates is indifferent to the user because hot water should always
be available when you need it with the Hot Water Lobster Instant Hot
Water Valve. Be aware that most pump systems: are restricted to
timers or cycle buttons before the pumps will circulate the water.
Which means hot water may not always be available during off times or
at sinks without start buttons (when you may need it); during pump
cycles, your entire cold water pipe is filled with hot water (as the
water returns to your water heater), and because hot water is pumping
for the entire time period, you cannot get cold water until after the
pump stops. pumps often only last 18-24 months before replacement is
necessary; initially the noise level of pumps is minimal but over time
can become very noticeable (especially when your trying to sleep);
pumps often cause electrical interference to televisions and radios;
and installation is more complex requiring a nearby electrical source
and electrical connections (to power the pump). On the other hand
the Hot Water Lobster Instant hot Water Valve: incorporates the
flexibility of an adjustable thermostatic control; is built with
quality materials and workmanship for a long maintenance-free life, is
easily installed (not requiring electrical wiring, timers or
perishable pumps); and is completely silent. There are so many
variables from plumbing system to plumbing system, calculating a
standard energy saving formula would be difficult and very complex. In
general, instead of replacing the water (wasted down your drain-while
waiting for hot water) with cold ground temperature water (which has
to be heated from a low temperature), the Hot Water Lobster Instant
Hot Water Valve allows already warm water to circulate back to your
hot water tank for reheating-which not only saves the cost of the
water, water treatment charges (sewer charges), it also takes less
energy to bring the already warmer water (being re-circulated) up to
temperature. The more often hot water is used the more energy is
saved (compared to not recirculating the water and heating ground
temperature water instead). Pipe heat loss is minimal compared to the
cost to heat 2-4 gallons of ground temperature water the 18-24 times a
day (the average family uses hot water). And in cold months (when hot
water is used 42% more often than in hot months) the heat loss is not
wasted (any radiant heat provided by the hot pipes transfers to heat
for your home). With or without a hot water recirculating system, the
better insulated your pipes are the less energy is wasted.
Best Answer
I suspect you have a set-up like this?
You are concerned that when the water gets pumped back into the "water heater" it could possibly pollute your main water line?
The only thing I could suggest is putting a check valve on the "cold" water supply so that it can only supply fresh water. That is helpful if the pumps output pressure is higher than your supply pressure (This could happen on someday with low supply pressure or if you do not have main water pressure regulator)
In this situation the return is a dedicated port on the "water heater/boiler" and there should already be a check valve/pressure regulator/non return valve just before the water heater. So the rest of the house will run just on the cold water supply and never get any recirculation contamination.