What can I do about runoff water from my neighbor’s property that is being directed by an existing pipe into my new driveway?

Your question raises the possibility of some interesting & complex legal issues. Unfortunately, your brief description of the facts involving the driveway & the adjacent properties does not permit a specific & complete legal evaluation of the case and the applicable law.

It is possible that your case may raise issues with respect to easements & nuisance.

You state that you have no easement, but you did not indicate whether you reached this conclusion after reviewing the deeds & the property records for both properties, in order to verify whether an easement of record exists with respect to your driveway.

Your description did not indicate how long your driveway was used for ingress & egress, during the time there was unobstructed access to it across the neighboring property. You did state that you've been the owner of the house for 10 years & that the existing driveway was used since the "house was built". It is possible that you may have a claim for an easement by prescription, even if there is no easement recited in the deeds or otherwise legally recorded.

A party seeking to prove entitlement to an easement by prescription over another property, has the burden of showing "...by clear and convincing evidence its adverse, open and notorious and continued and uninterrupted use … for the 10-year prescriptive period. Aubuchon Realty Co. v. Cohen, 294 A.D.2d 738, 739, 742 N.Y.S.2d 421 (3rd Dept., 2002).

Since you have admittedly owned the property 10 years, you may be able to raise the argument in court, that the 10-year prescriptive period was satisfied by you during your 10 year period of ownership & that an easement by prescription has been satisfactorily established by you. If you are successful in a lawsuit against your neighbor, the judge would enter a court order declaring that you have an easement by prescription. In that event, you would not need to incur the expense & potential problems regarding water drainage & property damage issues involved in building a new driveway. You should seriously consider consulting with an attorney who practices in this area of law before going thorough the time & expense of constructing a new driveway.

If an attorney advises you that you have no viable legal options regarding the existing driveway & you decide to build a new driveway, your neighbor's refusal to divert water runoff onto your property from his drainage pipe may give rise to claims by you for private nuisance, continuing trespass & property damage. If the court determines there is a valid nuisance claim, you may be entitled to an injunction from the court in order to stop your neighbor from allowing the drainage water to runoff onto your property.

These are admittedly complex areas of real estate law, so again, I strongly suggest that you give serious consideration to consulting with an attorney who practices in these areas of law, so the attorney can thoroughly review all of the necessary documentation, as well as the applicable law.