Easement for services

We have recently discovered a fault in our property, where water does not drain properly from a garden bed.  This is a critical flaw, as if too much water collects, it flows into our basement and even our meter room.

A company has quoted on correcting the drainage problem, but it means running a new pipe along the ceiling of some lots' garages.  The design of the building means there's unlikely to be any other way of getting the water out.

Our strata manager has advised us that we need to have easements drafted and filed, at a cost of several thousand dollars. They say that it's not enough to just get written permission from the owners (which the owners are happy to provide).  We're pretty keen to get this resolved quickly, and avoid unnecessary costs. 

My question is: Why is it not enough to get written permission from affected owners to install the pipe?

Secondly, there are a number of other (original) services in lot owners' garages.  These are not recorded on the strata plan, and as far as I am aware there's no easement for them.  Are these potentially problematic too?