This study shows that distillation in large dual plant is still compet
itive with seawater reverse osmosis, for Middle East conditions. Howev
er, if energy costs are high, such as in Europe, and the USA, reverse
osmosis becomes increasingly attractive. A distillation plant is gener
ally more tolerant of difficult seawater conditions and severe operati
ng conditions than RO when membrane performance and life can be advers
ely affected by silt or contamination of the feedwater. Multiple effec
t distillation is well established for the small to medium size range.
The lower capital cost and auxiliary power consumption make MED compe
titive with MSF, even though a larger number of units are needed. MED
plants is now a major contender for all but the very largest installat
ions. MED has greater potential than MSF for high performance ratio de
signs. An RO plant has considerable scope for future development in te
rms of membrane performance and cost reduction. RO is likely to be the
main contender in high energy cost areas.