A conservative estimate would be 3 urinations a day multiplied by 32,000,000 Canadians multiplied by 12000 mL (6L models are mandatory in Ontario in new construction since 1996, but are certainly not common yet) TOTALS 1,152,000,000 litres of drinking water FLUSHED every day! Yep, that's over ONE BILLION LITRES. Your personal contribution would be 3.6 litres/day, or 1314 litres per year. This, in my mind, is unacceptable. And so... we've adopted this rule:
Assuming our household works like most other households, Meghan and I use the toilet at nearly the same times twice a day, first thing in the morning and in the evening. The last one to leave the house in the morning flushes the toilet, and the last one to pee at night can do the same. We could be more anal in our approach ;) but this method minimizes the 'gross' factor and the smell from urine sitting all day in a small space. On top of that, I've adjusted the float valve in the toilet tank so that our flush volume is less.