This study investigates the green business development case in Finland, which was born as a result of the Onsite Wastewater System Decree (OWSD) entered into force in 2004, changed in 2010 and totally renovated in 2011. The study concentrates on the SME companies producing and selling equipment and services related to the individual waste water package plants. The business development is observed as a SME based business opportunity with great potential, but heavily influenced by the external factors like the legislation, the political climate and the recent economic recession. The business development is measured by new product performance indicators. The results show the real business volume of this niche green business field, the overall business development trend and SME managers’ experiences and understanding about the external factors during the operational years of the decree in 2004 -2010.