Shower Water Tank Question

I want to do a shower that uses it’s own specific tank in conjunction with a fresh water tank and a gray water tank, in this type of way. Use a “middleman” shower tank so once I’m clean I can run that and just stand in it without wasting water.

I shave at the sink and have shaving cream all over my face before I get in the shower

I get in the shower turn it on and have an entrance knob that is set to use the fresh water tank, I have another knob that sets the exit water to go to gray tank.

I use soap and wash that off while all the shaving cream soap mixture heads towards the gray water tank down the drain until I’m clean.

I then turn my exit knob so that the water now goes to the SHOWER tank and I let it run for a short bit

I then turn my entrance knob to pull from my SHOWER tank, and keep the exit knob also set to shower, so now it is just cycling the shower tank water.

As I’m finishing up I can chose to turn the exit knob to Gray water tank to empty the shower tank, OR I can just leave it alone and when I shower next time I can empty the shower tank into the gray tank as I wash shaving cream off of me.

Or of course I could flip back so using fresh water to end the shower off perfectly clean from fresh water.

What are your thoughts on this?

I would need 2 pumps and 2 hot water heaters I assume?

what about delays for the hot water heaters to heat the water that might cause a problem?

thanks so much for your help


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Greetings & Welcome!

Well… This is the first time I’ve heard of this scheme, and I have to tell you that I like it a whole lot better than the other recirculating shower ideas I’ve seen. A big kudo’s for that!

I’m thinking that a Y with a diverter valve before the water pump, with one leg going to fresh and the other going to recirculate would handle it with a single pump & water heater. Followed by a second Y after the drain, with a Y diverter valve on it going to the grey water tank or the recirculation tank.

I’m thinking the recirculation tank could be pretty small too… Of course all tanks will need to be vented.


“Everything should be made as simple as possible." ~ Einstein

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thanks so much!

I have been thinking about this more and the hot water heaters I’m seeing take about 20 minutes to heat up the water so if I am switching inputs wouldn’t this be a problem?

Would I need one of those hot water heaters that don’t use a tank?


As much as I hate propane, the simplest route might be to go with a tankless propane water heater.

I too occasionally enjoy long hot showers, especially in the winter, but my system is very old school, combined with a newer drop in style shower hose. I use a storage bin to catch my shower water, so it’s easy to drop the battery operated shower hose/pump/head into it instead of clean water. With enough water to cover the shower pump, I can have as long of a shower as I want.

I heat my water using a fire coil (sometimes also referred to as a shower coil), on my stove, heater, or even in a campfire, and just recirculate the water through it. This gives me endless hot water until the batteries in the shower pump fail. Since I’m only wanting a shower rather than washing/cleaning, the water stays clean. It only takes maybe a couple gallons of water for that endless hot shower.

For a treat, I have a rubber boat that I can take to the shore of the ocean, a lake, or river, and fill it with water and have a 1-2 person hot or cold, hot tub or jacuzzi. I have this USB powered water agitator that is designed to be used in a bucket or barrel for laundry, that’ll stir up the water like a boat motor would, only safely.

Did I mention that I honestly enjoy my lifestyle? :slight_smile: I sometimes get accused of being too old school, until they actually come and camp with me… :wink:


“Everything should be made as simple as possible." ~ Einstein

wow I love how you do it. It’s so “minimalistic” and not so reliant on so many systems!

So for me after learning more about these electric hot water heaters, for example the 4 gallon one. It is not like you can only shower for as much as 4 gallons will last because it mixes the really really hot, hot water with the cold water depending on your shower knob position that you set.

So really it’s more like 7 gallons of water that you can shower with, which is a good shower time, but you could do it even longer with more water if you pull from the recirculated shower tank instead of the cold fresh water tank temporarily.

So I think my system could still work with 1 pump and 1 hot water heater.

  1. The hot water heater only pulls from the fresh water

  2. pump pressurizes the whole system, hot water heater water, fresh tank water tank, and my shower water tank.

  3. the Y diverter digital actuator valve would be at the junction of the cold fresh water tank, and the shower recirculated tank.

  4. I choose in the shower when I want to switch between the two

so while it’s not my exact idea from the start this way I think can work!


That might work. I like as simple as possible. :slight_smile:


“Everything should be made as simple as possible." ~ Einstein

do you think I would need a second pump so 2 water pumps in all, one for each tank?


I think a single pump should work. With a Y between fresh & shower, then self priming pump, then Y between cold & water heater.

If shower water goes back through water heater, that could help keep the temp comfy too.


“Everything should be made as simple as possible." ~ Einstein

sorry I forgot to mention I will be going with a 4-5 gallon electric hot water heater and not doing anything with propane or an instant hot water heater.

So I think the heater needs about 20-30 minutes to heat up the water so it would need to already be heated from the fresh water tank in order to have hot water right?

if I want to keep my hot water tank free of my shower tank water, I can’t think of a way to only do it with 1 pump. If I only use 1 pump then at some point in the switching its going to be pumping shower tank water into the hot water heater I think.


Probably don’t want to put anything but fresh water through a hot water tank.

Have you checked on how much power would be needed for an electric water heater/tank? 1500w @ 12v = 150a draw. That’s a lot.


“Everything should be made as simple as possible." ~ Einstein

yes of course only fresh water in the hot water tank.

I’m trying to first solve my problem of how to accomplish my goal of using a recirculating shower tank before attacking a completely different problem later on about how many batteries and which of the many hot water tanks available I will choose.


I usually approach things from the opposite direction.

A) Can it be done without electricity?
B) If not, what’s the minimum power usage possible.


“Everything should be made as simple as possible." ~ Einstein

The theory behind how this would work does not depend on how much electricity or the minimum power.

I would like to solve this theoretical problem, but I don’t think this forum was the right place to ask.

This is a bit fancier but there is nice diagram of the system itself.

Once I saw a great idea regarding hot water heater. One van had electric heater that would only heat water when van was driving, it either had a large alternator or second one installed for that purpose. Water stays hot in the insulated container for a long time.

Obviously that alone won’t work if you stay in one place for extended periods. Then a generator would be an option.

oh that system is awesome!

yes that is a bit fancier but the theory is in the same boat as my idea!

thank you so much.

I think what I’m going to do is build the system (miniaturized) with small 5v cheap pumps and see if I can get something working.

thank you so much for this, it’s awesome!

As you noted, there’s no way of doing this with one pump, as once the water is in the shower it is gray water and would contaminate pump and piping if connected back through any part (pump, tubing, fittings, etc) of the clean side of the system (which probably includes the water heater unless it’s only for showering water). From a plumbing/engineering perspective it’s a cross connection/backflow prevention issue. Typically such systems use a specialized backflow prevention valve which is basically two check valves in series with an air gap that opens between them if the downstream check valve to the gray system fails. Note that a check valve or even two alone is NOT suitable on its/their own for a potable water system - there MUST be an air gap (which could drain back to shower or gray water) in case of valve failure. While two simple check valves with anti-siphon might solve the backflow issue, it sure seems like a two pump (fresh and recirc.), 3 tank (fresh, recirc, and gray tanks) system would be needed. The biggest challenge then is how to keep that recirculated water warm for a prolonged shower without a second heater or heat exchanger. Even with filtration prior to the heater, you could have fouling problems due to soap, dirt, body oils, etc).

The advanced-rv dot com 2 gallon shower in the linked video is awesome, as are most all the features in their $300K+ B class vans 8~/. Just keeping it in perspective . . .

thank you so much for your input and I do need to learn about how the valve system would work when and if this idea ever comes to fruition.

In the video that was linked above, He quickly says “the auxilary heater” which is what he uses to reheat the water.

I’m wondering if you might know of what I should search for in order to see what this type of heater is and how it works in terms of timing.

This guy has Bosch electric heater.

Another cool (or warm) idea could be a calorifier that circulates engine coolant while you drive: calorifier tank campervan - Google Search

Here’s one that heats the tank with engine coolant, there is apparently an addon for using also diesel air heaters (that would be running anyways at cold weather) AND it can be fitted with an electric heater… (mains power = generator) or was that a standard feature? Anyways…

I was also thinking about how to make the secondary heater working. One idea could be routing the recirculating water through the water heater tank in a separate loop (as in: instead of using engine coolant to heat method, run shower water in those pipes) to re-heat water. Or both, if you would build the tank yourself.

Inre: SureJust Calorifier. This is what I’m going to install in my build. They are a proven tech and have been used on boats for many years. It uses a coil that taps into the engine heater hose loop (I will put in a heater control valve to turn coolant flow on/off) that heats the water in an insulated tank (@ 22 liters/6 gal in my build). The well insulated tank stays hot for several hours. The water gets heated to engine coolant temp (185°F) in about 1 hour of driving. There is a mixing valve on the output to mix with cold to supply hot water at the desired temp (I’ll go with approx 115 to 120°F), then on to shower, sink, etc. It also has a 120VAC 1000 watt heater element for use on shore power or generator that will heat to about 165°F (which should take about 1 1/2 hours without running the van). After mixing this system should supply two short showers worth of warm water, approx. 12 gallons. This will drain to a gray water tank.

There are twin coil calorifier units that could possibly lend to using one of the two coils as a reheat coil for recirc shower water. The intended purpose is for a second engine coolant loop or aux. hydronic heater, but it might work if the flow isn’t too great and it’s only raising the temp enough to keep already warm water warmer.

Pretty interesting stuff. I’ve learned a lot about boating equipment since starting this van build. Many of the problems and the platforms and tech they use are transferable.

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