A methodology for the environmental impact evaluation over the life span of a Domestic Solar Hot Water System (DSHWS) is presented. The results are compared to the environmental consequences of the conventional energy form substituted and the total environmental gain is calculated. For the purposes of this analysis, the "Eco-indicator '99" Life Cycle Impact Assessment methodology was adopted and the materials and procedures of the DSHWS production and utilization are evaluated. (C) 2003 Elsevier Ltd. All rights reserved.