In response to issue 1 in your question.
I located this description
Turf systems can be either filled or unfilled. A filled system is designed so that once it is installed, a material such as crumbled cork, rubber pellets, or sand (or a mixture) is spread over the turf and raked down in between the fibers.
Read more: http://www.madehow.com/Volume-7/Artificial-Turf.html#ixzz356epI24D
Since the base or filling may conatin soil underneath the blades, I can see that there may be a problem with watering astro turf in such situations. If you are certain that the base is not soil, then watering is not a problem.
Regarding issue 3 - Marit Ayin - In many cases turf looks like real grass. I think most people agree to this. Make your own judgement when you watch a baseball or football game on TV. (The argument that TV distorts everything is not really true these days with HDTV.) It looks real at first. My own opinion based on this is that it would be marit ayin as it is NOT obvious to all that it's turf.
On the other hand, there could be a separate issue of "cleaning" if the turf is extremely dirty....