I scraped my knee badly and now it hurts to get water on it?

We were messing around at my friend's house and I (very stupidly) got on the back of his treadmill while somebody else was on it, long story short I fell and the treadmill basically sanded my right knee. It didn't bleed, just stung a lot and went all red/pink and shiny and moist. When I got home I cleaned it as best as I could with a tiny amount of water, drizzled from a cotton wool pad rather than directly from a tap or shower, and it stung REALLY badly. I don't know how I can cope with a shower this morning if even tiny trickles of water were so painful. Any ideas?