Thanks I'll try them. Any other advice ?
You need a softener before r/o to remove those calcium and magnesium deposits in the water.
I heard a story that the council (who supply the water to Hartlepool) have to treat the water to one of the industrial estates. I don't know how true it is, but it could be worth doing a few tds tests. (If they are, then the likely hood is that they will be returning the waste water back into the supply line.) You maybe able to link in with someone who has a unit in there if this is the case.
There are a few windies in that area using wfp, so what are they doing? CNC is from Hartlepool and occasionally comes on here. His name is Justin and he had the same issues as you about 3/4 years back. He had a Vivaro etc van in those days if my memory serves me. He said his water was around the 550 mark.
Your issue with regard to low pressure will be calcification of your water pipes restricting flow. For me I would try to find a small unit in Billingham area which uses a different water source.