Dehumidifier water should be fine for the radiator, but don't make the mistake I made and use it in the windscreen washer of your modern. I suspect the water contains dust and mould spores pulled out of the air, which would appear to happily breed in the lukewarm washer bottle and coat the inside with black slime !

My Uncle once lived in southern Spain and used to sell dehumidifiers amongst other things. He visited one customer "out in the sticks" who proudly showed him how he drank the stuff (to save money on bottled water). In view of the above, rather him than me !

Location: New Forest