Historically speaking dragons have often been associated with water. They, like any top predator, would secure for themselves that most valuable of resources and defend it. They would often establish a burrow or occupy a cave close by their chosen water source. Whether that water source was a town well, watering hole, dam or lake did not bother them. Understandably this would often lead to conflict. First with farmers who were used to not having to contend with a ferocious wall of scales, claws, teeth and flames whenever they lead their cattle to water. Then followed shortly after by a brave knight, or two or three (Depending on the size and ferocity or the dragon). These cases almost always led to the eventual demise of the dragon, and the reclaiming of the precious water source hopefully unspoiled by toxic dragon blood.
In our day, water is easily accessible in most first world countries. I would imagine that very few wonder if they can safely secure a cup of water. This bounty has worked out great for modern dragons who are smart enough to figure out our complex water storage devices.