Why? It's only the UN. All nations are not members. Canada could very well sign something that says each person has the right to water.
"Let them come and get it. Oh shucks, they can't afford to come get it? Then perhaps some generous companies could set up desalinization plants in those countries."
Canada donates enough to countries in need.
Wel, I haven't read the document. If by right to clean water is meant that governments can't stand in the way of other countries getting access to clean water through free trade, then maybe we should sign onto it... if we intend to abide by it of course. But again, if it's just for the photo op, then no we should not sign onto it.