Legal Question in Real Estate Law in New York

Yes. In order to draw water from your neighbor's well, you would need an easement over your neoighbor's property to obtain the water and convey it to your premises. If both houses were owned by the same person, and that person installed the water system and then conveyed away the house that did not have its own well, the purchaser of that home would have a good lawsuit if the water were shut off, but in the meantime (several year-long lawsuit) you could not live in the house for lack of water. So you would deal with this issue, we may hope, before buying the property.

Even if the present owner is a person you have known for years. What happens if he/she dies, goes bankrupt, gets Alzheimer's and the children never like you anyway.....

Don't buy without an easement. Even if the new neighbor is a saint on earth.