GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Solenoid valve for the toilet hookup?

BrianWL | Posted in Green Building Techniques on

Dear Martin, et al:

Having just changed the flapper valve in a toilet after my water bill was high due to the unappreciated running of the commode, I am wondering why we don’t have a better system for toilets? Specifically, why not a valve such as one finds in a lawn irrigation system?

For $15-18, one can get a lawn sprinkler system valve, which of course, is in the default: off; no flow setting. Add a 24 volt solenoid, it turns on, allowing flow. This, with the appropriate 24 volt AC adapter, could be wired to the light switch of the bathroom. When the light is on, then there’s water and the toilet fills. When it’s off, the toilet would not run and run and run thereby wasting a whole lot of water.

This does not sound cost effective until one considers the sensor switches that are installed to run light bulbs. My LED 60-watt-equivalent bulb says it uses $1.08 per year in electricity. Yet, there are plenty of $59.99 sensor switches installed to run that bulb…I would contend the break even cost of this common electrical convenience is much worse than preventing a toilet that runs and runs (or for that matter, a broken washing machine hose).

What is right or wrong with this idea?
Thanks, Brian in Austin

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    Most homeowners aren't going to do this, because (a) it costs money to install, and (b) it's one more thing that might go on the blink and need fixing. But, if you like to tinker, nothing is stopping you from installing such a valve at your own house.

  2. jberks | | #2

    Hi Brian,

    I see your point. Hey, I personally love rethinking things. But I'd have some questions

    How much does the clapper valve actually leak? Has it been measured?

    The standard toilet clapper and refill system is not the most robust mechanism but its certainly cheap and reliable enough. We know it works, especially if there is a power outage. With this system, the weak link is the clapper and how it seals the outlet. Idustrial design of each specific toilet would play a role in this. Also, most toilets have a low flow fill valve, which is one of my pet peeves to have to wait for the cistern to refill. I believe this was designed to alleviate pressure issues with a traditional trunk and branch plumbing design.

    Maybe a re-think of the mechanical system itself is worth a look?

    Can you get a heavier clapper to get a better seal?

    Personally I love the raised cistern toilets with the chain. Lots of height for greater head pressure to flush with. Put in a spring-closing valve and chain for the flushing mechanism instead of a clapper system and you won't be getting any leaks for years. Mechanically its beautiful.

    Maybe look into a pressure assisted toilet. I don't have a lot of experience with them, but based on their design, I'd imagine they maintain a positive pressure seal on the topside of valve. Also, they use less water, and if you run a manifold plumbing system to the toilet, I'd bet getting a good 1/2" line with up to 80psi to the toilet will help with this as well (including refill time).

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |