Pure water is not a good conductor of electricity; however, water containing soluble salts will conduct electricity roughly in proportion to the quantity of salt present. This relationship is accurate enough to determine the salt concentration by measuring the electrical resistance or the electrical conductivity of a solution. In this procedure, the electrical conductivity of a soil-saturated paste extract is used to estimate the amount of soluble salts in a waste∕soil.

To determine the soluble salts, the soil is extracted with distilled or deionized water. The salts dissolved will increase with increasing waste∕soil:water ratio. Salt determinations normally are based on conductivity of an extract of a waste∕soil when at saturation, called saturated paste extract.