Paint reaction to water...... HELP!!

I wasn't sure whether to place this in here or bodywork but here goes…

I've got myself a clipper that before I purchased it, had been resprayed.

There seems to be something wrong with the paint on the bonnet and the scuttle panel, but the rest of the car seems fine.

Basically, when the car gets wet (by rain or washing) the paint reacts with the water and leaves a sort of fade in the paint like a water mark which seems virtually impossible to get rid of. I have previously cut the paint back with a heavy grain rubbing compound and this removed it, but then the next time it rained it was back again. Obviously, I can't keep cutting the paint like this or I'll have no paint left.

Any ideas on what may be causing this, or how I can fix it will be greatly appreciated. Failing this, guess I'll have to start saving for a respray job. :-(

Thanks in advance.

Gav

My opinion is maybe a single stage respray has been done, which basically oxidises and gets marked very easily due to no lacquer being applied. (unless you can tell or verify paint/clear coat job)
Only thing to do its to clean/polish and then wax or seal to help keep it fresh for longer. Wolfs body wrap is meant to be a longer term sealant but I'm not clued up with sealants!
A PH neutral shampoo may also help