Water Line Easement in Backyard

[Yin Lee]

We were recently notified that there is a water line under the back yard of our to-be built house. The sales agreement we signed a couple of months ago did include a map of easements, but it did not show anything in the back yard. The builder admitted they provided inaccurate information, and they proactively helped the home buyers affected by this issue to get exceptions allowing us to build a fence and plant shrubs on top of and beyond the easement line (but we still can't plant tress). hence, they refused to reimburse us furthermore. The easement is cross over at 1/3 of the back yard (a pretty small yard). How much does the property value will be affected by the water line?  Is it worthwhile to get a lawyer involved?