My siding needs to be pressure washed and I need to know what kind of cleaning solution to add to it. Or is it better to just use plain water? The humidity where I live causes a film to build up (mold? mildew?) and I don't feel like paying someone to do it. It only needs to be done once a year, but I figured if I bought a pressure washer I could likely find some other projects to use it for around here.