Since it is a cross lease there won't be any easements, as you both jointly own the land. Check with the council if they have it recorded that both properties are fed from the same meter. You will probably have to tell them the meter serial number to be sure. It is very common for cross lease properties to share the same water meter or connection. (you are after all sharing lots of other stuff as well). This will at least mean that when the council starts billing for water, they will just split the bill in 2 and bill each owner for half the usage.
Depending on how many people live in @Paul1977 house compared to the neighbours. The shared pipe might work out better. As for water flows, see if what you get currently complies with the building code NZBC G12 see paragraph 3 table 5.3.1
There are still a surprisingly high number of cross lease and body corp properties in Auckland that that are on shared pipes. Despite the really high watercare usage charges. At least it means that leaks get fixed.

