This happened to me this weekend! My friend invited me to go swim but I was so hesitant about it because of the acne scars on my back! Imagine having to cover that up! The night before, I even tried to conceal them with a heavy duty concealer to see if it wouldn''t look weird, but they ended up looking worse and orange to my great dismay I knew that if I didn't go swim, I would have a shitty day just staying home by myself when I could have gone out and have fun! Just think to yourself that you'll have fun at the water park, I think you'll be more uncomfortable wearing makeup than not wearing it because it would get wiped off easily by the water (unless you are very extra careful about it, to the extent that you don't have fun, that would be bothersome, wouldn't it?). I was still super self-conscious about my back, like I would always put a towel around me or I would go in the pool after my friends so that they don't see my back, I would crouch low in the pool so that my back is hidden in the water....
I totally understand you about wearing makeup everyday and being dependant on it. I was like that for a about a year. I felt that once I stopped wearing it, I felt more free and careless. Makeup was an additional thing to worry about (keeping it from smudging, melting, greasy,etc.). Now I only reserve it for special occasions or whenever I have some place to go out to. Maybe you should start slowly, like instead of wearing makeup every day, wear it where you would feel more uncomfortable (perhaps school, work...) and don't wear it where you feel more comfortable, where you feel people won't judge you (like at a friend's house).
My daily routine:
Morning : Wash face with Cetaphil Oil Control Foam Wash, moisturize with Cetaphil Oil Control Moisturizer w/ spf30
Before bedtime: Wash face with Cetaphil Oil Control Foam Wash and apply Tactuo on affected areas
Medication: 100 mg Minocycline/day
Primer: B.Kamins Corrective Mattifier
Foundation: Mary Kay Timewise Matte-wear foundation
Set: Revlon Photoready Translucent Finisher