CA may be a bit odd as to eminent domain ..but using it to benefit a private developer on non blighted properties may not be in the cards at all.
Unless you can find some existing easement broad enough to cover water lines ....I think you may find it cheaper and safer to buy his lands or pay his price for an easement ....once your well runs dry your barter power hits about zero and his price may well go up. I Don't know what is lawful in your area ..but big water tankers are quickly big expense items !

