Hooked up to the parks water line.  Had used an On-the-go water softener but still had the problem.  Don't know if getting a whole house filtering system would help or even getting a RO system.  Could the problem possibly come from the Blue RV Drinking water hose?  I know when I used the cheap White hose, scum would build up so started to replace them 2-3 times a year but the hose was out in the direct sun, while 90% of the Blue one is hidden under the RV except for 5 foot each end.  Or do I go for PVC drinking water quality pipe and just use a couple of foot of hose going into the RV?