Nothing wrong with accepting a drink of water from a customer. That they gave it to you warm-ish .... meh ... maybe straight from the tap? Maybe they didn't have any bottled water cold?
I find that the more affluent the customer, the less likely I am offered even a drink of water. Had one SOB shadowing me on a really hot day at his shore front house with his yacht in the backyard dock on the canal. He kept chugging his tall cool drink clanking the ice cubes. Watching me and chatting away. I am sweating from all pores of my skin. Not even an offer of a drink from the hose. As I am cleaning up and putting away the tools, he takes off w/o a word. Guess he didn't want to pay the bill.
Other obviously less affluent and most likely less able to afford it customers .... I've been offered drinks, food, and even a tip.
I do not accept booze though. If I am offered soda or ice tea, I'd ask for water. Better for you on a hot day. I bring my own gatorade and water, but if a customer offers I accept.