Just chiming in to second (5th? 6th?) what others have said. I wouldn't be too worried. Typically in situations like this you, as the owner of the land subject to the easement, have the right to continue to use the easement area in any way that doesn't unreasonably interfere with the rights of the easement holder. So, from the sounds of it, I wouldn't say that you are "violating" the easement at all.
In my neck of the woods (which, admittedly, is not your neck of the woods), its very common for fencing/sidewalks/driveways to be installed over top of a waterline easement. Basically anything that's not a permanent structure. (Side note, the landscaping might be a touchier subject - if its something with deep roots that could interfere with the water line that could be an issue, but doesn't really sound like it is in your situation.)
Who bears the cost or expense to replace a section of sidewalk or fencing that's overtop of the easement, you or the easement holder, if it needs to be torn up might be an issue, but probably not a big one. As Fishindude mentioned, in my area, the easement holder likely is only required to regrade and replant grass/resod. Anything improvement-wise above that is sort of a "use at your own risk" type situation, where the landowner will likely be responsible for the costs to repair. Though, the easement document itself should specify who is responsible for what costs.
Sorry, this response got long and is more than you're asking for I think, but, is the easement of record? If so, I don't think you even need to worry about disclosure, because it's already publicly available. I'd mention to your realtor and probably wouldn't really worry too much more about it.