Terry, you can easily shoot those from the gutter, even on a windy day with the bandit.
As for the water I have never had anyone say anything about it. Just tell them that you can either use their water or tack on an extra $50 per house to haul in your own. The amount of water used wont even put a blip on their bill anyways.
The condos we've done, we've gone through the HOA's also and the managers deal with the homeowners concerns. Just make it abundantly clear on your bid that if anything is damaged that you are fully insured and will be held responsible for repairs. Make sure when you send in your bid be very thorough. Include
1. Your method
2. The precautions you take to protect the clients property
3. Copies of your insurance (WC and Liability)
HOA's like to have all of the info right up front and not have to search you down for more info.
As for price, im not sure what your prices are in your area, but for just the front of a building like that and taking into account that there are 50 of them, I would charge somewhere around $225-$250 if they have gutters and $275-$300 if they dont have gutters.
On the bid I would break it down per building, per unit, and total cost for the entire job. It just eliminates any questions.
If I can think of anything else, ill post it