ive just tested my water straight from my tap in my flat and its 27tds!can it change regularly?as it was 70tds before xmas!as most of u know ive not gone wfp yet.could i clean with 27tds without resin then?just tap water? 
well mine ( in my post above ) was 037 and dried spot free
though at 027 it will not cost you much in resin over the year