Design & DIY

What are the guidelines for buying “low-flow” toilets?

What are the guidelines for buying “low-flow” toilets? Do they have any effects on septic tanks?

In Ontario, low-volume or low-flow toilets (those that use six litres of water or less per flush) have been part of the Ontario Building Code since 1996, but a lot of low-flow toilets – whether or not they carried the Canadian Standards Association (CSA) stamp – required two, or even three, flushes to clear, defeating their water-saving purpose.

The Canadian Water and Wastewater Association (CWWA) tested hundreds of CSA-certified low-flow toilet models and published its final, exhaustive report, titled Maximum Performance Testing of Popular Toilet Models, and it contains more than you ever wanted to know about toilet testing. But it does tell you, via simple-to-read tables, how much waste each model handled in a single flush. The differences are astounding: Some models removed far less than 250 grams of solids (the report’s recommended minimum for certification), while others removed several times that amount.

Even after you’ve chosen a proven performer, you (or a plumbing professional) need to ensure that your cottage’s plumbing is suitable for a low-flow toilet. Potential problem areas – especially if your system is older or was a DIY job – include badly designed drains, improperly installed connection fittings, and a horizontal drain line with too little or too much slope. (The correct slope for a 3- or 4-inch drainpipe is 1/4 inch per foot.)

As always, the less waste water you send to your septic system, the better, so a low-flow toilet is a good option. Each flush, however, sends out the same concentration of bacteria and other organics for the system to deal with, and the amount of grey water from your other plumbing fixtures won’t change, so the Ontario Building Code won’t be cutting you any slack: You’ll still need the same size of septic system.