highlight that the percentage of water loss
via ET is directly proportional to the difference between vapour
pressure at the leaf surface and vapour pressure in the overlying
air. As a consequence, the greater the leaf surface, the greater the
vapour pressure of the leaf surface and the pressure difference
with surrounding air. It is clear, therefore,that further knowledge
of typical ET values of the species used in the treatment systems,
based on environmental conditions in the CWs, is essential in arid
areas where itis necessary both to ensure high pollutant-removal
performance levels and limit water loss via ET. Various techniques
have been developed regarding ET estimation in order to provide