The distance from the center of a circle to its edge; one half of the diameter.
Rate of Flow
The quantity of water flowing past a designated point within a specified time, such as the number of gallons flowing past a point in one minute – abbreviated as gpm.
Red Water
Rust-colored water. Such color is usually due to the presence of precipitated ferric salts or to dead microorganisms that depend on iron and manganese.
Residual Bromine
The amount of measurable bromine remaining after treating the water with bromine. The amount of bromine left in the pool or spa water after the bromine demand has been satisfied. Includes hypobromous acid (HOBr), hypobromite ion, free and total bromine and all combined bromine.
Residual Chlorine
The amount of measurable chlorine remaining after treating the water with chlorine. The amount of chlorine left in the pool or spa water after the chlorine demand has been satisfied. Includes hypochlorous acid (HOCl), hypochlorite ion free and total chlorine and all combined chlorine.
Rust
A reddish corrosion product occasionally found in water. Rust is formed as a result of electrochemical interaction between iron and atmospheric oxygen in the presence of moisture. It is called ferric oxide.
