Over time, rain jackets use their waterproof ability. There are things you can put on the jacket to make it waterproof again, but I've found it to be only moderately successful. Is there anything that can be done to prevent the waterproofing from wearing off?
If you have a waterproof jacket with a membrane like gore-tex. there is nothing you can do. If it´s puntured you can seal those but when the waterproof membrane is damaged over a large area or damaged trough general use or washing with the wrong dispersion - it had it´s time. Worked at an outdoor-outfitter, so i can back this up.
I usually spray down my jackets with outdoor Scotch Guard after they start absorbing water and I do not have any problems repelling water for many wash cycles thereafter. I have used the regular stuff before such as Scotch Guard designed for clothing, but it does not work as well and typically cost the same as the outdoor version of it.
Rain Jacket losing waterproof ability?
Nothing is perfect.
Rain jackets will lose their ability to be waterproof over time. That is a given. But one can prolong the end result by only rinsing them in water by hand without laundry soap and letting them drip dry! I hang them in the shower for this.
If you have a rain jacket like Viking pictured below, it is good to spray it will ArmorAll to best keep it waterproof.
Normal jackets once cleaned and dried can be sprayed with a waterproofing compound. I would recommend a Nikwax product.
In my experience, the spray-on products I've tried only worked for one shower of rain and then the jacket went back to allowing water to seep through. However, I have also tried the products that you wash into the jacket, after washing with a special detergent, and the re-waterproofing lasted much longer (about a year). I made sure to remove all traces of washing powder from the washing machine first, by removing and cleaning the drawer.