Hardness refers to a characteristic of water primarily caused by calcium and magnesium salts. The Baylis curve shows the relationship between the pH and the alkalinity of the water and provides a tool for establishing chemical feed rates in order to avoid deposition and corrosion. Drift is a change in an instrument reading over a change in time. All measuring instruments have drift and must be re-calibrated in accordance with time to a standard to provide reliable results. Hysterersis is the phenomena of having two different readings as opposed to the standard or known in the same instrument when the values are measured from opposing ends on a scale.
Density is the mass of an object divided by the volume.
Conductivity is the ability of a substance or material to carry or transmit an electrical current. Volume units are given in cubes such as cubic feet or cubic meters. One cubic foot is equal to 7.481 gallons. A drop test refers to a method of measuring the flow of a filter bed in a water treatment facility by closing the influent valve and observing the volume loss in a specified time. Public water systems must be able to provide enough flow and pressure to fire fighting equipment without damage to existing systems or loss of water service.