Some companies sell water brooms as a surface cleaner. Well, in my opinion they are not! It's like calling a floor broom a floor scrubber. Don't get me wrong, water brooms are a great tool. Just don't go buying one thinking you can remove a years worth of moss and algae from you patio. You will need a true surface cleaner for that job.
First, a water broom has multi nozzles. We learn from our nozzle chart that the larger the total orifice size is, with the same flow, the lower the pressure will be. So, if you push your water through 3 nozzles (some water brooms have 4) the total orifice size will need to be the same as the one nozzle you use. OK, so let's ay you do that by installing 3 smaller orifice nozzles in your broom to maintain pressure. Now you still have full pressure but 1/3 the water coming out of each nozzle. Works good for sweeping and rinsing, but not so good for cleaning. The smaller nozzles are also much more susceptible to plugging. Make sure you keep all your fittings clean as well as your water. A high pressure inline filter will help keep the nozzles from plugging up.
Second, a water broom directs the pressurized water forward, not straight down like a surface cleaner. This forward action is great for rinsing, sweeping leaves and debris, but does little to clean a dirty surface.