I do not consider talk of rainwater harvesting is off track when talking of bore holes and costs
and remember there is NO cast iron warranty on how deep they need to go to find a suitable clean supply of water
there are lots of other ways to make ranwater drinkaalbe part form a a slow sand filter -
Even if you have a bore hoile you still need to make it safe to drink WIth at least UV and maybe other things depending on mineral content of the water
one close to me had to have extra gadgets to get rid oF a small amount of arsenic in the water .
there is no where in uk where there is not enough rainfall that harvestinbg would not work --If you use national average for water consumption of 150 litre per person per day and 2 people
then a 4 week of NO rain would mean you would need a tank of a minimum size of 12000litres ----to have an emergency reserve ..
If money is a consideration --then examine that option --my guess it would be well under 10k
even with bore hole you will have maintainence and pump replacements now and then .
and bore holes can dry up as well.
I am considering this as my plot would need a pumping station to get it up the 100mvertically and 500m horizontally to the house ,so guessing at £15k and 10year replacement of pumps @2k for parts.
I would get mains connection to my site at bottom of hill next to main road --then its up to me after that with pump station and elec supply from house down to it
the attraction to going mains is no maintainence for me ,and if i want to build some holiday homes then i would need even more storage capacity if own supply from rainwater --30000litre ?
looked at borehole --and costs were estimated at £15k for 130m deep hole in granite --,but again no warranty .
they could find enough water at 40m --do you feel lucky?
I would certainly want to use a contractor that has done boreholes in your area already
I went off that cos my plot is right next to my quarry and that has water coming out of rock faces ,so i am suspecting that could effect how much water I would get from bore hole as some of underground water is already escaping into my quarry lake
plus i know in summer the flow is much less into the quarry