Health issues with recirculating hot water?

[scherzoja]

Are there any negative health aspects of recirculating water from the water heater back to the fresh water tank?

I am thinking of recirculating the hot water while I wait for it at the shower. Rather than wasting that water or using a bucket to capture it, I might recirculate it back to the fresh water tank.

Any virus/bacteria issues that are unique to hot water thanks on boat that would make it unwise to recirc back to fresh water tank?

Thanks

[PirateGuy]

Next time you want a drink of cold water, do you spit out the pee warm water coming from your taps?
I believe most residential systems recirculate back to a hot water tank. My personal opinion on boat systems is very KISS.

[GILow]

Originally Posted by scherzoja

Are there any negative health aspects of recirculating water from the water heater back to the fresh water tank?



I am thinking of recirculating the hot water while I wait for it at the shower. Rather than wasting that water or using a bucket to capture it, I might recirculate it back to the fresh water tank.



Any virus/bacteria issues that are unique to hot water thanks on boat that would make it unwise to recirc back to fresh water tank?



Thanks

Legionella comes to mind for a start.

[sailorboy1]

Originally Posted by GILow

Legionella comes to mind for a start.

This wouldn't change whether there is, and the danger of, Legionella.

Other than the element complex I see an issue with what the op wants to do. I nothing use that first cold hot water to wet and wash my head as my head doesnt care if the water isnt hot yet.

[bensolomon]

There are no organisms that would grow in your water heater water that would not also grow in the the main water holding tank, as well. Tap water is not sterile, and will contain micro organisms, in general. Usually, though the load of the organisms is so low, they don't cause disease (coliform bacteria), or the organisms don't cause disease in immunocompetent people (mycobacterium avium, cryptosporidium).

Ben

[GordMay]

Although Legionella bacteria can be found in natural water sources (lakes, rivers and streams), as well as in the ground, the main sources of infection remain artificial water sources, like water-cooling towers, spas, or water heaters.
Legionella bacteria multiply especially well at temperatures ranging between 90° F and 115° F (32°C and 45°C).
Any temperature that will minimize scalding, in accordance with temperature limits in the plumbing codes, will be in the Legionella bacteria growth temperature range.
The only solution to this dilemma is to use hot water temperature control valves, to keep storage and distribution temperatures above the Legionella growth temperature range (140° F ➛ 150° F, or 60° ➛ 70° C), and reduce the temperatures, at the fixtures, to a safe temperature for bathing, showering and washing.

The proper way to design a domestic hot-water system, to control Legionella and scalding, in that order, would be to store the hot water at about 140 F to 150 F. That temperature will kill Legionella bacteria in the water in the storage tank and distribution piping system.
Then, the proper design would use a mixing valve that will accurately deliver hot water to the distribution system at 134° F.
The circulating pump size/flow rate, and hot-water system insulation thickness should be designed with the recirculation piping limiting the flow velocity to a maximum of 3 feet per second, at a 10-degree temperature drop in the circulated loop so that the hot-water return temperature is at or above 124 F. The reason for a minimum of 124 F hot water return temperature is because in the new ASHRAE 188 standard, Legionellosis: Control of Legionella in Building Water Systems, suggests a hot water distribution temperature no less than 122 F (Legionella bacteria stops growing about 122 F)

[tkeithlu]

We have hot water circulation not back to the fresh water tank but back to the water heater. Wanting hot water from an only 6 gallon heater and wanting to conserve water, we press the push button switch near the faucet/shower head for ten seconds. That activates the circulating pump. It does mean a more complicated water system - there is something of a maze of PVC pipes in the engine room, but it works quite well.

Reqarding the concerns posted above, water that has passed the original fresh water pressure located at the tank is used first, although some of it does circulate in the hot water loop before use.

[Izikalvo]

Legionella, absolutely, if you drink from your water tank, don't mix.

[sv_pelagia]

Not that we normally have to do it here in British Columbia, we got into the habit of filling our kettle with cold water at the shower (before it turns hot).

Water in kettle is always boiled, so no issue there.

[Cadence]

Sounds like a great idea to conserve water usage.

[sailorboy1]

Bet only person in this thread was trained and certified in Legionella :whistling

The OP has no extra Legionella danger from his plan. But boats are great Legionella breeding grounds if someone wants to start a thread on that topic.

[CassidyNZ]

In my experience it takes more water to set the temperature to an acceptable level than it does to get hot water to the shower. When one considers the amount of water in the pipe, 5 meters of 1/2” pipe contains less than a half a litre of water. So to get hot water from the califont to the tap hardly generates enough water to make the morning coffee. I’m pleased that I have enough water reserve to not have to capture that in a bucket/kettle/bottle.

I have seen on large super-yachts, systems that continuously circulate hot water water around the vessel but this is more aimed at convenience than water-saving. The passenger on a $100m boat doesn’t want to wait for hot water to travel down 30 meters of pipe to reach his shower, it needs to be there the moment the tap is turned on.

[GILow]

Originally Posted by sailorboy1

..

The OP has no extra Legionella danger from his plan....

Good to know.

[scherzoja]

Thanks for the input. Sounds like I should have no issues if I keep the water potable. Just in case, I will probably capture in a bucket/pot or put in a hot water recirculation circuit that runs it back to the water heater, not the potable water tank. That means one more pump and I have to design it so if that pump fails I can still use the catch-bucket method. A little more complicated,
but that's better than running afoul of any thermophiles.

Thanks again,

[PirateFoxy]

Originally Posted by sv_pelagia

Not that we normally have to do it here in British Columbia, we got into the habit of filling our kettle with cold water at the shower (before it turns hot).

Water in kettle is always boiled, so no issue there.

I am stealing this idea for our RV.