Water quality and environmental conditions on the vast majority of Heating Ventilation and Aircondition Cooling Tower applications permit acceptable service life from standard Cooling Tower construction using the materials previously described. Significant deviation from these "normal" conditions often demands alternate materials choices.

For most purposes, the following criteria define "normal" conditions:
Standard tower design assumes a maximum of 120 °F hot water to the tower, including system upset conditions. Temperatures over 120 °F, even for short duration, may impose damaging effects on PVC fill, many thermoplastic components, galvanizing and plywood.Those rare applications demanding hot water in excess of 120 °F usually benefit from careful review with the tower manufacturer to assure that appropriate materials changes from the standard configuration are included in the initial purchase specification.

"Normal" circulating water chemistry falls within the following limits (note the distinction between circulating water and make-up water):
pH between 6.5 and 8.0, although ph down to 5.0 is acceptable if no galvanized steel is present. Low ph attacks galvanized steel, concrete and cement products, fiberglass and aluminum. high pH attack wood, fiberglass and aluminum.

Chlorides (expressed as NaCl ) below 750 ppm.

Calcium (as CaCO3) below 1,200 ppm-except in arid climates where the critical level for scale formation may be much lower.

Sulfates below 5,000 ppm - if calcium exceeds 1,200 ppm, sulfates should be limited to 800 pp, (less in arid climates) to prevent scale formation.

Sulfides below 1 ppm.

Silica (as SiO2) below 150 ppm.

Iron below 3 ppm.

Manganese below 0.1 ppm.

Angler saturation index between -0.5 and +0.5 -negative LSI indicates.

Corrosion likely ; positive indicates CaCo3 scaling likely.

Suspended solids below 150 ppm if slides are abrasive-avoid film - type fills, if solids are fibrous, greasy, fatty or tarry-wood, PVC, Polypropylene or ABS fills can be used, but PVC usually is the material of choice.

Oil and grease below 10 ppm or loss of thermal performance will occur.

No organic solvents.

No organic nutrients, which could promote growth of algae or slime.
Chlorine from water treatment 0 below 1ppm free residual for intermittent treatment; below 0.4 ppm free residual for continuous chlorination.
These conditions define normal circulating water, including the chemical concentrating effects caused by recirculation of the water to some predetermined number of concentration.