On 11 Feb, 14:58, "Sumgod" wrote:

Situation: Water supply comes from a well (old brick 'tank' approx two
metres deep and one and a half across built over a spring).

Built over a spring? Are you certain or is it belief acquired with the
house?

The reason I ask is that this sounds like a brick cistern. They were
built to collect rain water from the house gutters and paved yards.
It's usable 'grey' water, but not suitable for drinking. You could
check by putting food colouring, or drain tracing dye in the gutters.
I've never heard of a cistern built on a spring, but I'm not Dr.
Drivel so don't claim to know everything.

You could consider a sand filter, it would take the coarse particles
out and prolong the life of cartridge filter. They are similar to
water softeners (i.e., they are water softeners) , but filled with a
suitable sand and not resin. The control valve backflushes it at
intervals and flushes the debris to drain. There are other types used
in swimming pools and aquaria. I seem to recall that green sand was
the filter media to remove iron salts.

There's lots of info on the internet from the USA. There are lots of
rural wells in use out there.