High-Efficency Toilets vs. Dual Flush: The Controversy #ItsADirtyBusiness

Play the 6min Podcast above.


I remember when I was a kid that I heard something on Owl TV and was convinced. I ran into the kitchen, grabbed a 1.5L mason jar, seal and lid, filled it with sand from my sandbox, and put it inside the toilet tank AND TOLD NO ONE I DID IT. Probably a year later, my Mom was cleaning something and noticed the jar in the tank. “COREY SHANNON KLASSEN” she yelled from the bathroom “What have you done to the toilet?”. I was 6 or 7 years old (30 years ago) and you can still do this but make sure it doesn’t interfere with flushing or add weight to the tank (which will cause it to leak.)

Back in the day, we could do whatever we wanted without recourse. Toilets had a flush rate of 10-12 Litres per flush (LPF) and as our population grows and water consumption increases, the demands on our environment are strained. At 100 litres of water used per day to manage our human waste puts additional strain on our municipal management systems. That math comes out to 36,500 liters per year or 2,628,000 litres in our average lifetime just to move our crap around and keep things sanitary.

A little known topic in the design and specification of bathrooms is the Dual-Flush toilet and its’ relationship to water conservation in building code standards. Did you know that your toilet is a major offender of water waste and with a frequency of use of about 10 times per day it wastes over 100 litres of water? That pales in comparison to the 2-4 litres of water per day that is recommended that we drink.


Dual Flush Toilets used in residences have 2 flushes that use 6.0 Lpf for big flushes and 4.1 Lpf for the little flush. These toilets usually have a top-take button flush (but let’s be honest because no one really knows which button is for what and if they just used “poop” on one and “pee” on the other, we’d get it.) Dual-Flush toilets saved about 40% of all that water usage.

High-Efficiency Toilets (HET) have a maximum flush rate of 4.8 Lpf (Litres per flush). These can not be easily spotted to the untrained eye, but a big give away is the single handle. HET’s use 20% less than Dual-Flush toilets, so that’s a 60% water reduction per flush!

It’s worth noting that commercial (or public use) toilets are different, but that’s not for here or today.

The Building Code has Changed

Since April 2010, all toilets installed in British Columbia residences must be High-Efficiency Toilets (Information Bulletin No. B10-02 April 29, 2010) because they use 20% less water than Dual-Flush Toilets. This means that every toilet that goes into a residence is 4.8 Lpf or less.

The Results Are Better

  • Dual-Flush and HET do the same thing. Move human waste.

  • A HET does not leave more skid-marks. Humans do that.

  • A HET does not take more time to clean. Humans make that mess.

  • An added 20% reduction in water consumption is the right thing to do.

  • Less water use is a lower water usage bill.

  • Earn cash by switching - City of Richmond and Creston have a toilet rebate program

If you want to geek-out on toilet studies, here’s one that was done by Gauley Associates, Ltd. and Koeller Company back in 2018.

Welcome to my first installment of “It’s A Dirty Business” topics where I explore the bathroom activities and building code regulations that affect what we do in our bathrooms. This isn’t a regular series or a set timeline, it will pop up as I work through my professional day as a Certified Master Kitchen & Bath Designer.

Follow along with the hashtag #ItsADirtyBusiness.