ALGAE IN URBAN DRINKING WATERS IN NE SPAIN

Tap waters from Barcelona and several other locations in N.E. Spain we re analyzed to determine the algal occurrence and to assess their prob able origin and fate. In general, a low number of taxa (2-9) occurred per sample, while cell density was highly variable (from 20 to more th an 1000 cells ml(-1)). Green algae were usually the most abundant, mos t of the taxa being common in natural phytoplankton assemblages from m esotrophic or eutrophic waters. The proportion of planktonic to benthi c taxa differed between samples, there being only one sample (Lerida) with a predominant planktonic composition. Analysis of treated water r evealed that algae were not completely removed at the end of the treat ment, meaning that a low number could reach the distribution network. Moreover, other organisms (flagellates) had their origin in storage wa ter tanks. No seasonal pattern of occurrence was apparent since there were many occasional taxa, implying a lack of direct connection betwee n natural populations and tap water algae. It is therefore suggested t hat algae can reach the distribution network by several possible origi ns. Algae were sometimes viable; culture experiments showed occasional growth in June, but not in August samples.