A composition for treating a water system to remove scale, microorganisms and biofilm, and corrosion by-products. The composition comprises chelating agents and a surfactant. Depending on the water system being treated, the composition may be a solid dissolved by water in the system being treated or may be a pre-mixed foam or aerosol. A treatment system particularly suitable for flowing water systems comprises a container for holding such a treatment composition and mixing it with a portion of water from the water system, a filter for removing solids dislodged during treatment, and a corrosion monitor. A method for using such a treatment composition comprises draining substantially all existing water in the water system, filling or rinsing the system with fresh water, contacting the treatment composition with substantially all parts of the water system, and draining the treatment composition from the system before resuming normal operations.
