Have you ever been awakened in the night to the horrifying realization that you accidentally left your RODI system running? You rush groggy-eyed through your house in hopes that this nightmare somehow isn't real. SPLASH! As you step into the utility area, garage, washroom, or wherever you have your unit mounted, your foot lands in a growing flood of purified water which has (at least) left you with an enormous mess or (worse) resulted in a flood that has ruined flooring and/or property... Or perhaps you come home to find that you failed to turn off the water which was being made and now you have to explain to your significant other why there is water all over the floor...(again?)

If you're like me, you've left the water on and overfilled the container...more than once! Even if the water is contained by a sink and doesn't make a huge mess, you still end up putting perfectly good deionized water down the drain, not the mention wasting deionizing resin. I don't know about you, but I HATE going through all of that trouble to make high purity water only to waste it! This is a simple solution I have implemented to prevent the accidental overfilling of DI water containers.

The total cost of parts is around $20 if you buy them on Amazon. You will need the following:
  1. 1- 12V, 500mA power supply (https://www.amazon.com/KEYWANTS-Sup...1-spons&keywords=12v+500ma+power+supply&psc=1)
  2. 1- 12V, 4.8W solenoid valve with 1/4" tubing ends (https://www.amazon.com/gp/product/B016MP1HX0/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1)
  3. 1- 12V float switch (https://www.amazon.com/gp/product/B01LZ09XPD/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1)
The assembly instructions are pretty simple:
  1. Clip the end off of the 12v power supply cable. Solder the positive (red) end to one of the leads on the switch.
  2. Solder the other lead of the switch to one of the lugs on the solenoid valve.
  3. Solder the negative end of the power supply cord (black) to the other lug on the solenoid valve.
  4. Rig up a bracket to hold the float switch in the desired water container. Ensure that the float on the switch is below the top of the container to ensure the switch activated before the water overflows. Mount the switch in the container. I used a piece of leftover starboard plastic that I built my filter sock holder from. I would recommend plastic of some sort to avoid contaminating the DI water with metal ions (if considering a metal bracket) or chemicals that may be in wood (if you're a carpenter).
  5. Install the solenoid valve in the water supply line going to your RO/DI unit. Pay attention to the flow arrow on the bottom of the valve to ensure proper solenoid orientation.
  6. Plug in the power supply and turn the water on. The water should flow through the solenoid but stop when the float on the switch is pushed to the upper stop position.
I used heat shrink tubing to cover the soldered connections. You can use the same, electrical tape, or liquid PVC tape to provide some insulation over the soldered connections. You could also use spade lug connectors on the solenoid valve if you wanted. I preferred to solder since it is more secure (but certainly not pretty!).

When power is lost, the solenoid valve automatically returns to failure (closed) position. Also, note that the maximum working pressure for the solenoid valve is around 120 psig. If you have higher water supply pressure than that, you will need to source a suitable valve.

While this is no substitute for secondary containment, it should help prevent unwanted waste of DI water.

You can experiment with the float switch style and you will need to rig a mounting bracket for you particular DI water container. If you want to get fancy, you can even order a 2.1mm x 5.5mm female pigtail (https://www.amazon.com/SIM-NAT-5-5m...&sr=8-2&keywords=2.1mm+x+5.5mm+female+pigtail) and solder this to the switch and valve, thereby eliminating the need to clip the end off male end of the 12V power supply.

Alright, here is the unit assembled (minus the power supply):

Here is a compatible 12V power supply:

Closeup of the float switch and mount:

I just place the white disk over the large opening in my 6-gallon water jugs.

Note that the switch can be disassembled for insertion into your custom mounting bracket:

Here is the underside of the solenoid valve. Note the flow arrow right is the center of the valve body:

Hope this is helpful in assisting you in avoiding future RODI flooding disaster. :)

Happy reefing and thanks to my wonderful daughter Caitlin for helping!!