I tried to fill my empty canteen in a pond, but the option did not appear. Had the canteen equipped but nothing happened. This was at the big pond , first one from the right that you see over here: http://dayzdb.com/map#6.079.120
After I moved East I tried it at the pond JUST left of Prigorodki (http://dayzdb.com/map#6.079.120), there it worked. I filled my canteen and moved into the village of Prigorodki only to return to this pond minutes later. The options to drink from the pond or fill my canteen (even though I completely drank it's content) did not reappear.
I'm suspecting a pond or water source can be only used/adressed ONCE untill the server restarts. Perhaps another player was at the first pond I was at.