This article summarizes the results of a materials and equipment review conducted on 13 operating geothermal district heating systems. Most of the systems included in this work have logged a minimum of 4 years operating experience. As such, they have encountered many of the problems likely to occur as a result of fluid chemistry and initial design. The purpose of publishing this information is to provide the operators of existing systems and designers of new systems with the input necessary to make informed decisions' regarding equipment selection and system design