sensors for use in the shower

i am trying to make a shower head that detects when someone is underneath it. So my question is what sensor would be best to do this?

and how accurate they are because i would quiet like to map where people are in the shower. i am happy to have multiple sensors that work together for that though.

Thanks

Hi,

You want "UNDER the shower" not just "In the shower enclosure" ??

PIR sensors would probably see moving hot water..

IR beam across the area under the shower seems better. Might try semi-waterproof units like these:

http://arduino-info.wikispaces.com/InfraredBeamPair

Use a camera. People would love that. Point is, would you want to see a strange device looking at you when you're nekkid?

By saying that you want to MAP where people are, does that suggest this a big communal shower? You need to be a bit more clear in your description.
PIR or IR would be fine just for detecting a presence in one spot. Automatic sinks, toilets, urinals, use plain infrared, while the bathroom lights use pyroelectric infrared. Mapping is a whole different project that will involve a camera or an obscene grid of sensors just to know where a naked person is standing in a room.