In a softener or deionizer it is the adsorption activity possessed in varying degree by ion exchange materials. This quality may be expressed as kilograins per cubic foot, gram-milliequivalents per gram, pound-equivalents per pound, gram-milliequivalents per milliliter, etc.. It can also refer to the ability of any media to take up a specific contaminant; that is expressed as time over gallons. When used as to flow rates, it is the maximum or minimum flow obtainable under given conditions of media, temperature, pressure, velocity, etc. For ion exchange water softeners, the capacity is expressed in grains of hardness removal between successive regenerations and is related to the pound of salt used in regeneration. For filters, the capacity may be expressed in the length of time or total gallons delivered between servicing.