The water table is the level below which the ground is full of water.
Ground water is underground water where all the pores in the soil are filled.
For example, when you dig a hole at the beach, you hit water very fast. A refractometer measures salinity of a substance by refracting the light through the substance and measuring the amount of light that is bent by the salt particles. You look through the end with the eyepiece, to see the amount of salinity. A lysimeter is a siphon. Darcy's Law states that the rate of flow is proportional to the length of the flow path.