Rarely do developers get to build on completely flat
land where everyone is affected equally by the fall of water from
the heavens. Most often, one neighbour will be higher or lower than
his neighbours and that inevitably brings into play the immutable
law of gravity.
Suppose we are buying land that is downhill from another
person's property. In that case, we have to expect there is
going to be some flow of water down onto our property, and good
building practice will ensure that as a low-side neighbour, we will
include some adequate measures in our own yard to make sure we
aren't too badly affected by this inevitable flow.
It is not always the case, though, that as a low-side neighbour,
one must accept the water as it comes and where a higher neighbour
does something to their land that changes the natural flow of
water, which causes the water to flow in a more concentrated
way.
