The 'Rock' of Gibraltar is a small isthmus at the western end of the Medite
rranean Sea overlooking the Straits of Gibraltar, the North African Coast a
nd Spain. For the last 1,000 years Gibraltar has been a strategic military
location guarding the gateway between the Mediterranean and the Atlantic Oc
ean. Water has always been in short supply on the 'Rock'. In olden times ra
inwater was collected, and earlier this century the Rock was partially cove
red by a concrete sheath to aid natural catchment. During the last 40 years
rainwater has been supplemented by a variety of seawater desalination proc
esses and the remnants of some of these early desalting plants can still be
seen today. The 36,000 inhabitants, made up of Gibraltarians, tourists and
military personnel have a daily requirement of 4,500m(3)/d of fresh water,
supplied from several sea-water desalting plants owned by the Ministry of
Defence (MOD) and the French water utility, Lyonnaise des Eaux. The main pr
oduction centres are the 1,680m(3)/d seawater RO facility at Glen Rocky and
the North Mole installation producing 2,400m(3)/d by MSF evaporation and 4
80m(3)/d by seawater RO. The remainder is supplied from an MED plant attach
ed to the local refuse incinerator, with an output determined by the volume
of refuse to be burned. This paper reviews the long-term operation of the
seven 240m(3)/d seawater RO units at Glen Rocky. It discusses alterations a
nd improvements made to chlorination, flocculation, scale control, and prod
uct water treatment. It details the way chemical costs have changed during
the past 12 years without jeopardising output or quality. It also details i
ncreases in chemical costs due to implementing improvements associated with
Health and Safety legislation. The paper also considers a few of the unfor
eseen problems the operator has experienced. Although Gibraltar is no longe
r a NATO base, fresh water is still a prime need for the population. Water
supplies could be met by laying a pipeline fi-om Spain, bur the desire of e
very nation to be self-sufficient in water coupled with long-term political
differences between Spain and Gibraltar precludes this option. Gibraltar h
as entered the new millennium as the only part of Europe with a population
totally dependent on seawater desalination.