In most areas of the world, water is withdrawn from a watershed and not put back, either because it is transported to another watershed or is allowed to evaporate. That is indeed water use, the kind that leaves the mighty Colorado River in the USA a mere trickle as it enters its former delta, the kind that will leave the Dead Sea of the Middle East a dry salt plain within a few generations, the kind that reduced the Aral Sea to less than 10% of its former area.
But in Ottawa, we don't use water in this sense at all.
For a start, the OECD treats the entire Ottawa River as 'used' 12 times between its source and mouth - by hydro dams that return all the water they 'use' straight back to the natural channel within a distance of a few meters. That's not use the way most countries use water.
Next, most of the water we remove from the Ottawa river at our municipal water intakes at Britannia and Lemieux is returned to the same river a few kilometers downstream at Green's Creek. And, it is there returned sufficiently unpolluted that it can be safely drunk. That's not use the way most countries use water either.
Not only that, most municipal water that is not returned to the river at Green's Creek is used to water farms and lawns. Much of this soaks into the ground and returns to the Ottawa River via groundwater. Before European settlement, most of the area of today's City of Ottawa was wetland, much of which is now kept drained with the drainage water going to the Ottawa River or one of its tributaries. The part we use to water green plants simply restores some of the drained water to our land. Water evaporation and groundwater flow from our watered spaces are still much less than the natural conditions prior to settlement. Ottawans could use far more water for this purpose than they do, and still not be using water by comparison with natural conditions.
Of course, we use energy to pump that water, to build and maintain water pipes, sewage lines and treatment plants. But, we don't use water here. Watering green space during our usual summer dry season keeps it in the health it used to have. That reduces the perceived need for lawn pesticides which cause so many health and pollution problems for us. Watering green space keeps it absorbing carbon dioxide as it used to, to reduce our contribution to global warming. Far from feeling guilty about it, we Ottawans on municipal water should be doing more of it.