If you are seeing water under the sink it's either from a leaky drain or water supply (or did I misunderstand your descrip)?
There are like 20 different fittings in the water supply and the drain, so you'll have to check each one. Dry both assemblies and the floor beneath thoroughly with a towel. Then turn on the water full power, and feel each joint with your finger for building moisture.
Most of these fittings will be compression/threaded fittings, so you should be able to solve any leak with a little tef-tape and retightening.
Am I missing something here?