why is my car emitting quite a bit of water on the garage floor after I use it?

Your air conditioner will drain water onto the floor as part of it's normal operation. The hotter and more humid the weather, the more water you can expect to drip. That's the humidity it's removing form the air to make you comfortable inside the vehicle. Also, your exhaust tailpipe will normally put out water for a short time after a cold start. Once the exhaust system is fully warmed up, that will stop.