The first time I had to rent a meter (townhouse complex, 200+ HO's to negotiate water usage with) I was attentive to water usage expenses as it was a new expense for me. When I returned it the bill was something like $45 for a weeks work. For comparison, it cost about $100 to fill my 27,000 gallon pool.
Most people are concerned because they just don't know how much you use or what it costs. So, a little math goes a long way toward solving the problem.
5.5gpm x 60 min = 330 GPH.
Water is roughly $4/1000gal, so water expense is roughly $1.32/hr.
And that's for the pump running 100% of the time. Remember that you're not using any water when in bypass, so reality is more like 75-80% duty cycle for concrete, and 40-50% for housewashing. If you show them the numbers and the homeowner gripes about $1 worth of materials on a $200 job, give them a crisp green dollar bill to cover it. Or better yet, find a new customer as they will be a huge PITA.
All that said, I would provide water (and sandwiches) for $0.16/sq.ft. Not with a tank/travel though. I'd rent a meter or strike a deal with one of the residents. You get to use his water (cost - $1.35/hr) and you pay him $10/hr (or something like that). he wins, you win, association gets what they want.
