Something equivalent to manorial lordship. The title itself would be "senior water rights holder". The right granted by this heritable privilege is the right to first service. A first service which may result in an inferior holder of water rights not getting any water at all.
It's important to note that, at least some, constitutional scholars see a focus on an actual "title" as beside the point. A state can call Michael Jackson the "King of Pop" without violating the clause because this title does not actually grant noble privilege in any way. It's just a name. However granting a heritable privilege that is not available to anyone meeting a similar, non-heritable requirement (such as a driver's license, which is theoretically equally available to all), does violate the titles of nobility clauses even if no actual "title" is granted with it.
It's important to note that, at least some, constitutional scholars see a focus on an actual "title" as beside the point. A state can call Michael Jackson the "King of Pop" without violating the clause because this title does not actually grant noble privilege in any way. It's just a name. However granting a heritable privilege that is not available to anyone meeting a similar, non-heritable requirement (such as a driver's license, which is theoretically equally available to all), does violate the titles of nobility clauses even if no actual "title" is granted with it.
https://constitution.congress.gov/browse/essay/artI-S9-C8-2/...