Hi you can test water in lots of different ways depending on what your looking for. I work in the drinking water labs for a water company and in these labs we test for alkalinity pH, colour, turbidity (thats how many floaty things are in it), Organics ( Volitile organic compounds) which include pesticides and solvents nutrients which include ammonia, sodium flouide, calcium etc and Total organic carbons. I work mainly in the trace metals lab. So I use an instrument called an Inductively Coupled Plasma Mass spectrometer or ICP-MS to check for metals at very low levels ( parts per billion) This vapouriser the water in a very hot plasma (6000 degrees c) and separates the ions according to their masses. They can then be detected and quantified.