AUTOMATIC WATER SAVER CONSTRUCTION
By Andina Foster, firstname.lastname@example.org.
If you have ever been cruising, even with a water maker on board, you know how
precious fresh water can be. On Yandina, with four heads, the run from the hot water heater to
the aft head is about 60 feet of 3/4" pipe. By the time you run hot water back there for a shower,
you have wasted over 3 gallons of water. This is proportional on smaller boats but still an
We installed a 12 volt solenoid at the far end of the hot water line and plumbed the outlet
from this to a hose which returned to the water storage tank. Push button stations were installed
at each place where hot water would be needed. Now you can dump the cold water back into
your tank and use the hot water with a clear conscience. We got rather fancy with a relay and
holding circuit which was broken by a thermostat monitoring the dump water so the whole
process was automatic. Actually, a simple on/off switch at each station is all that is really
necessary as it is unlikely you will forget and leave it on.
Parts you will need.
- One push button for each head or place where you will need to use the water saver system.
We used a door bell type button, available at most hardware stores. It is nice to get one with a 12
volt lamp in it so when the lamp goes off you know the water is hot and finished recycling.
- One 12 volt DC relay with a normally open contact. It should be rated for 5 amps minimum,
mainly for long life. You should be able to find one at your local Radio Shack for a few dollars.
- One adjustable thermostat with a normally closed contact that opens as the temperature rises. It
should be adjustable and have a range that goes down to about 100F. This will detect when the
hot water arrived at the end of the line and turn the water off. The cheapest source is a hot water
heater thermostat. You will have to improvise on the mounting as most of the sensing area must
be in contact with the hot water. We ran the water through a section of copper pipe that had a
piece of flat copper soldered to it and the thermostat was clamped to this plate.
- One 12 volt DC solenoid valve. 1/4" Solenoid valve, about $22
- A 12 volt DC coil for the valve. These are rare but it so happens that the 24 volt AC coil which is readily available works just fine on 12 volts DC. 24Volt AC solenoid coil, about $19
- You will need a ball valve that is fitted at the end of the hot water line before the solenoid valve. This is used for isolating the automatic system if something goes wrong, for removing pressure for maintenance, and finally for adjusting the flow rate if necessary. I found that there is a time lag from the arrival of the hot water at the thermostat before the thermostat heats up and stops the flow. I was concerned about wasting some hot water but by reducing the flow it takes just a little while longer for the hot water to arrive but the thermostat is more responsive to shutting it off. Play with the thermostat setting and the flow until it works right.
- The positive supply circuit should come from a fuse or circuit breaker so you have protection if there is a short somewhere, and it is nice to be able to disable the system from one switch.