Water quality: How water is described or characterized. Water quality is a measure of how good the water is in terms of meeting its environmental values.
Water quality indicators: These are the different types of measurements that can be performed to describe water quality. Examples are nutrients, heavy metals, turbidity, bacteria and pH.
Water velocity: The velocity of water, usually measured as the change in speed over a unit of time (eg 2 metres per second) in a specific direction, usually horizontal in water treatment.