How To Measure If a Toilet or Showerhead is Low Flow or Not

Easy method to measure and find out exactly the flow or GPF – gallons per flush – your toilet is using per flush.

  • With a Sharpie marker or grease pencil, mark the water line in the tank of the toilet.
  • Close the water valve at the base of the toilet.
  • Flush the toilet.
  • With a gallon (or other capacity) water container, refill the tank, noting how much water it takes to fill the tank to the marked level. That’s it.

California building codes require toilets to be 1.28 GPF if brand new in 2023, but any toilet that flushes 1.6 GPF (or less) are typically considered ‘low flow’. The City of Angeles allows all existing toilets to be 1.6 GPF when selling. Different plumbers have different definitions of low flow, ultra low flow, super low flow, etc.

Showerheads – With the same gallon (or other capacity) container, estimate the amount of water after 30 seconds of flow, then double that figure to arrive at the showerhead GPM – gallons per minute – of flow. California requires showerheads to be 1.8 GPM of flow or less.

More on the 2023 state of California regulation when selling a home regarding toilets and showerheads here.

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