I can't imagine giving all and sundry an enforced power shower/free enema is going to help calm anyone down.
The point is that it's not all and sundry, it's those who are actively rioting, water cannon is I would suggest more directed than CS gas / rubber bullets.
We live in a society that allows protest, the consequence is that we must accept that some protests will turn violent and therefore have the means (where we cannot prevent the violence, by for example separating EDF/UAF) to deal effectively with wide spread serious public disorder.
