Most contaminants are coliform bacteria and faecal streptococcus, and among chemical ones, there are ammonia, nitrates, nitrites, rare heavy metals and other toxic agents.

In previous years, microbiological inspections detected most often contaminants as follows increased total or aerobic mesophyllic bacteria, E. coli and faecal streptococcus, while chemical analyses detected organic contents, ammonia, nitrate, nitrite, iron, and other toxic matters (disinfection processes by products).