Naaah, the leftists would love that. They're deluded enough to think getting hosed would make them the equivalent of civil rights heroes in Selma.
Instead of hoses, how about a riot-control device that emits painful blasts of noise. I remember seeing this used somewhere to good effect --it quickly disperses the ruffians without doing permanent damage. As long as the National Guard has good earplugs in supply.
Riot control weapons like noise, tear gas, pepper spray will also affect the innocent people in the crowd, and surrounding areas. It should be something that can be aimed at the disruptors.