Identifying the true cause(s) of building water system failures is critical to prevention, mitigation and where applicable, legal defense. Any system failure is generally the result of several, often complex, variables. Because of the specialized nature of chemical water treatment knowledge, chemical water treatment has become an easy scapegoat for a wide variety of system failure claims. However, the origin of these problems is frequently either unrelated to water chemistry, or water chemistry is just one of several variables contributing the failure. Common causes of system failure unrelated to water treatment include: (a) Operational Issues; (b) Design Issues; and (c) and the lack of Legacy Knowledge with respect to the system operation and maintenance practices. Operational causes of system failure may include: (1) improper commissioning; (2) inadequate cycling of the system; and (3) over-firing /or under-firing. Design issues leading to system failure may include defects arising from (1) material selection; (2) inadequate hydraulic balancing; and (3) velocity related erosion/corrosion. It is the intent of the authors that this understanding these possible causes will aid in identifying the root cause of the occurrence.