A dual flush toilet has two flush options: a light flush of about 0.8 to 1.0 gallons (3 to 3.8 litres) for liquid waste, and a full flush of 1.28 to 1.6 gallons (4.8 to 6 litres) for solids. Because most flushes in a household are the light kind, a dual flush toilet uses roughly a third less water than a single-flush toilet with the same full-flush rating, and a fraction of what the 13-litre toilets in most pre-1996 Canadian homes use.
This guide explains the mechanism, puts real litres and dollars on the savings for a Canadian family, decodes the ratings on the box, and compares dual flush with the alternatives so you can decide whether it is worth the small premium.
Quick answer
- Dual flush: 0.8–1.0 gpf light, 1.28–1.6 gpf full. Average per flush in real use is about 1.0–1.1 gallons (4 litres).
- A family of four replacing a 13-litre toilet saves roughly 60,000–70,000 litres a year, about $250–$350 at GTA water and wastewater rates.
- Look for a MaP score of 800 g or higher on the full flush and a WaterSense label.
- Dual flush one-piece toilets start at $208; premium rimless and wall-hung models run $500–$1,000.
How a dual flush toilet works
Every gravity toilet works the same way: the tank dumps water into the bowl fast enough to start a siphon in the trapway, and the siphon pulls the bowl’s contents down the drain. A dual flush toilet controls how much water leaves the tank.
- The flush valve is a tower or canister in the centre of the tank rather than the old flapper. Pressing the light button lifts it briefly and drops it early, releasing only part of the tank. Pressing the full button holds it open until the tank is nearly empty.
- The buttons are usually on the tank lid, one small and one large, or a single lever that you push up for light and down for full. Wall-hung toilets use a two-button actuator plate on the wall.
- The bowl is designed to clear with the smaller volume. That is why you cannot make a dual flush toilet by putting a dual flush valve in an old tank: the bowl geometry has to match.
Modern dual flush toilets from Toto, Duravit and our own MyBath line flush as well on the full setting as any single-flush toilet, because the engineering effort has gone into the bowl and trapway rather than the water volume.
How much water a dual flush toilet saves in Canada
Toilets are the largest indoor water use in a Canadian home, about 30% of the total. The savings depend entirely on what you are replacing.
| Toilet | Litres per flush | Family of four, per year* | Cost per year at $4.50/m³ |
|---|---|---|---|
| Pre-1996 toilet | 13–20 L | 95,000–146,000 L | $425–$655 |
| Standard 1.6 gpf single flush | 6 L | 44,000 L | $197 |
| High-efficiency 1.28 gpf single flush | 4.8 L | 35,000 L | $158 |
| Dual flush 1.28 / 0.8 gpf | ~4 L average | 29,000 L | $131 |
| Dual flush 1.0 / 0.8 gpf (Toto G450) | ~3.3 L average | 24,000 L | $108 |
*Assumes five flushes per person per day, 4:1 light-to-full ratio for dual flush. $4.50 per cubic metre is a blended water plus wastewater rate typical of Toronto, Mississauga and Ottawa in 2026; Montreal households on flat-rate billing see no direct saving, Calgary and Vancouver metered households see a similar one.
Replacing a 13-litre toilet with a dual flush model saves a family of four about 66,000 litres and $300 a year. The toilet pays for itself in under a year. Replacing an existing 1.28 gpf single-flush saves about 6,000 litres and $27, which is why we tell customers with a modern toilet not to replace it just for dual flush; buy dual flush when you are replacing anyway.
The ratings on the box
- gpf / Lpf. Gallons or litres per flush. Dual flush lists both figures, full first: 1.28/0.8 gpf.
- WaterSense. The EPA label, used in Canada too, for toilets at 1.28 gpf or less that pass an independent flush test. Most municipal rebate programs that still exist require it.
- MaP score. Maximum Performance testing measures how many grams of solid waste a single full flush clears. 600 g is the minimum to be listed; 800 g or higher means the toilet will not need a second flush in normal use; 1,000 g is the ceiling of the test.
- CSA B45 / ASME A112.19.2. The North American toilet standard. Every toilet sold legally in Canada meets it; it is not a mark of quality beyond that.
Dual flush vs single flush vs pressure-assist
| Dual flush | Single flush 1.28 gpf | Pressure-assist | |
|---|---|---|---|
| Water use | Lowest in real use | Low | Low (1.0–1.28 gpf) |
| Flush power | Good on full flush from a quality brand | Good; simplest to get right | Strongest; used in commercial settings |
| Noise | Quiet | Quiet | Loud |
| Parts and repair | Canister valve, brand-specific seal; $15–$40 part | Flapper or canister, universal parts | Sealed pressure vessel, $150+ to replace |
| Bidet seat compatibility | Fine; buttons on the lid do not interfere | Fine | Fine |
| Price premium | $0–$60 over single flush | Baseline | $150–$300 premium |
The three complaints, and whether they are still true
- “The light flush does not clear the bowl.” It is not meant to; it is for liquids. If you use it on solids you will flush twice, which is still less water than one full flush on an old toilet. Teach the household which button is which.
- “The buttons stick.” An issue with early budget models. Current Toto, Duravit and MyBath toilets use a cable or direct-push mechanism that has been reliable for a decade.
- “The tank leaks between flushes.” The canister seal wears like a flapper does, roughly every 5–7 years. It is a $15–$40 part and a ten-minute job; buy the brand’s part, not a generic.
Which dual flush toilet to buy
MyBath Dual-Flush One-Piece
$208.50
Elongated, soft-close seat included, 12" rough-in
Duravit D-Neo One-Piece Rimless
$499
Rimless bowl with no under-rim channel to clean
Duravit D-Neo Wall-Hung Set
$1,000
1.6/0.8 gpf in-wall tank, two-button actuator plate
For a second bathroom or a rental: the MyBath one-piece at $208 does everything a dual flush toilet should, includes the seat, and has no seam to clean. For a primary bathroom: Duravit’s rimless D-Neo, one-piece or wall-hung, adds a bowl with no rim channel, which is the single biggest cleaning improvement in toilet design in twenty years. For the full smart-toilet experience: the Toto Washlet G450 pairs a 1.0/0.8 gpf dual flush with an integrated bidet, and is the lowest-water toilet we sell.
Frequently asked questions
Are dual flush toilets worth it?
Yes when you are replacing a toilet anyway, especially an older 13-litre model, where the savings are around $300 a year for a family of four. Not worth replacing a working 1.28 gpf single-flush toilet just for dual flush; the extra saving is about $25 a year.
Which button is which on a dual flush toilet?
The smaller button or the smaller half of a split button is the light flush for liquids; the larger one is the full flush. On lever models, lifting up is usually light and pushing down is full.
Do dual flush toilets clog more?
No, as long as you use the full flush for solids and the toilet has a MaP rating of 800 g or more. Clogging complaints almost always trace back to using the light flush on solids or to a low-rated budget bowl.
How much water does a dual flush toilet use?
About 0.8–1.0 gallons (3–3.8 litres) on the light flush and 1.28–1.6 gallons (4.8–6 litres) on the full flush. In normal use the average works out to roughly 4 litres per flush.
Can I convert my toilet to dual flush?
Retrofit dual flush valves exist for old tanks, but the bowl was designed for a full tank of water and the light flush usually does not clear it. A purpose-built dual flush toilet at $208 performs better than a $40 conversion kit.
Are there rebates for dual flush toilets in Canada?
Most municipal toilet rebate programs ended in the 2010s as high-efficiency toilets became the norm. A few utilities still offer $50–$100 for WaterSense models; check your local water utility before buying.
Shop dual flush toilets
One-piece toilets · Wall-mount toilets · Smart toilets · All toilets. Not sure what fits? Read our toilet rough-in guide.
