I've been in a few houses outside of the UK where water comes from an untreated spring. (Sweden, France and Bulgaria). In every case the water the people living there have never had problems with it.
I've also known other properties with filter systems. They seem fine as well.
What I'm saying is that I guess it's a question of do whatever gives you peace of mind.
As to telling the FC - there's one simple rule to follow: never volunteer anything to anyone! Least of all an "authority".
Solar energy, wind turbines whatever it is then here is your place to talk about it.