The Drarga treatment plant was chosen as a pilot site for treatment and reuse of domestic wastewater. It uses reed beds as a tertiary treatment, so this research was conducted to study the performance of the reeds over a period of 3 years (March 2006–March 2009), that is three growing seasons. The reeds were cut after 2 years. Knowing that the Drarga climate is semi arid, we studied the behaviour of purification by reeds over seasonal changes. The reeds were effective in removing pollution over the three growing seasons studied; the average removal of BOD5 over 3 years was 71%. The maximum removal efficiency was in winter; this is associated with high oxygenation of the water mass caused by mixing and stirring induced by the movement of the long stems of the reeds.