Of course they do! - There is a joint U.S.-Canadian evaluation program called Maximum Performance (or MaP) that uses soybean paste encased in latex to see just how well these low-flow toilets work. And most of them work very well. Test results are easily accessible on the Internet. 

Todays Low-flow toilets don’t use any more than 1.6 gallons of water per flush.

High-efficiency toilets use even less water than standard low-flow models, some as little as 1.1 gallons. 

Dual-flush toilets, with separate flush modes for solid and liquid waste, are another water-saving option. 

Replacing an old toilet with a low-flow model is a simple and fairly inexpensive way of conserving resources—one of the pillars of green building. 

The City of Calgary offers a $50 reward - in addition to the $100’s more in future savings on your water bill - when you take out your current water guzzling toilet and replace it with an eligible low flow model.