It rains constantly here from October to May, and I don't use a waterproof jacket. I have a cheap Performance Century II jacket that I wear when it's below 60. Below 50, I add arm warmers. Below 40, I wear a long sleeve wool baselayer. It very rarely gets below 30 here.

For water resistance, you can't beat human skin. Manage warmth and avoid cotton and the water isn't an issue.