Algae in urban drinking waters in N.E. Spain

Abstract

Tap waters from Barcelona and several other locations in N.E. Spain were analyzed to determine the algal occurrence and to assess their probable 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 than 1000 cells ml^-1). Green algae were usually the most abundant, most of the taxa being common in natural phytoplankton assemblages from mesotrophic or eutrophic waters. The proportion of planktonic to benthic taxa differed between samples, there being only one sample (Lérida) with a predominant planktonic composition. Analysis of treated water revealed that algae were not completely removed at the end of the treatment, meaning that a low number could reach the distribution network. Moreover, other organisms (flagellates) had their origin in storage water tanks. No seasonal pattern of occurrence was apparent since there were many occasional taxa, implying a lack of direct connection between natural populations and tap water algae. It is therefore suggested that algae can reach the distribution network by several possible origins. Algae were sometimes viable; culture experiments showed occasional growth in June, but not in August samples.