The conductivity factor (CF) of dissolved salts in a given solution is a measurement of conductivity. Using the electrical conductivity between two electrodes in a water solution, the level of dissolved solids in that solution can be measured. Measurements can then be used to dose the solution with the necessary nutrients in the case of hydroponics. Conductivity measurements are also used in ecology and environmental sciences to assess the level of nutrients in lakes and rivers. For a discussion of conductivity in this context, see Total dissolved solids.