Please break apart my idea and find as many faults as you can.

[Lightspeed]

A couple of thoughts:

Observation: My understanding is that your house is in clear line of sight from your BOL. Is this correct? If yes, you'd only need reasonable quality optics to be able to observe it. A remote alarm system triggering a PMR radio alert ought to function well over this sort of range, alerting you to activity at the remote site, and allowing you to keep most of your attention on other BOL activities.

Water: How deep is the water table at your house? Do you know? If not get digging. A hole in the back garden will serve well to let you know how deep the ground water is. Leave the hole exposed for a whole year to see how the level rises and falls. If not too deep for you to reach with spade and effort type excavation, I'd consider doing two things ( in order). 1st get the water tested by a public health lab to see what's in it. 2nd, if the test does not identify any nasties you cannot filter/ remove yourself, consider lifting floorboards in a downstairs room and digging yourself a ground water well in there. You could cap it off and replace floorboards and leave as a contingency.

One thing to consider about ground water. It will tend to carry contaminants from higher levels to lower levels, so if your house is below the level of others in the area, what is clean water today could easily be contaminated with effluence if neighbours start building latrines and soak away cess pits in their gardens up-hill from you.