The number of wastewater treatment plants (WWTPs) in the Czech Republic is increasing. Wastewater, which was previously disposed of in other ways (e.g. septic tanks, cesspits etc), is now entering the surface water (after treatment at a WWTP). Billions of Czech crowns have been invested in the construction of new WWTPs or reconstruction and intensification of existing ones. This money had been invested to meet discharge standards for individual pollutants. However, the overall level of pollution associated with wastewater discharges has not been assessed. The indicator of grey water footprint was used to assess whether there was an increase in pollution load discharged from WWTPs between 2002 and 2018. Discharged pollution data from 4115 industrial and municipal WWTPs were analysed. The analysis of such a large data set has not been carried out yet and brings new knowledge concerning the effect of WWTP size on the grey water footprint. Overall, the total value of the grey water footprint (and thus of the discharged pollution level) decreased in the monitored period. Grey water footprint caused by the largest WWTPs decreased, while the grey water footprint of small WWTPs increased, due to the increase in their number. The decisive pollutants that determine the value of the grey water footprint are total phosphorus and ammonium nitrogen. Measures targeting these two main pollutants can significantly reduce the overall level of pollution load discharged from WWTPs.

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Surface water pollution is referred to be a problem in the entire Odra river basin. In sub-basins, an insufficient degree of wastewater treatment has been identified as a major problem – in relation to the best available technologies and environmental objectives of Directive 2000/60/EC. The grey water footprint indicator was used to express the influence of point sources of pollution (industrial and municipal wastewater treatment plants) on discharged pollution reduction in the Czech part of the international Odra river basin. The number of 391 records of wastewater treatment plants for the period 2004–2018 was analysed. The results show that the wastewater treatment plants reduce by up to 92% the potential water needs for dilution of pollution discharged into waters in the Czech part of the Odra river basin.

Citing sources is an important part of any research paper. A number of studies in the past have dealt with discrepancies or errors in citations. The citation errors range from several percent to tens of percent. Although in most cases, these are minor formal inconsistencies that do not prevent tracing the source used, there are cases where the citations are incorrect or refer to non-existent articles. In this study, an analysis of the citation of the grey water footprint definition was conducted. The water footprint concept was introduced in 2002 as a methodology for the description of quantity aspects linked to water use in the life cycle. The grey water footprint, which represents the quality aspects of water use, was added to the water footprint concept later on. In this study, almost 300 articles that provide a definition of the grey water footprint and are indexed in the Scopus database were reviewed. More than two-thirds of the articles added the definition by citing the source. Only 3.5% of the citing articles contained an incorrect citation that could be considered a significant error. Although this is a low number, these significant errors have been appearing only in recent years. This suggests the possibility that the percentage of errors could gradually increase as the use of grey water footprint expands in practice. In the first period (up to 2017), only the grey water footprint originators are cited. From 2017 onwards, papers not written by the originators of the grey water footprint idea are also cited.

Grey Water Footprint is an indicator of anthropogenic pollution load into the inland water. The indicator is used for quantification of water needed for pollutant dilution to such an extent that the quality of the ambient water remains above agreed water quality standards of pollution discharged from point sources in the Czech Republic. Grey Water Footprint was calculated for 6 382 point pollution sources, recorded in the national register of wastewater discharges, from period 2009–2018. The domestic, industry and agriculture sectors were analyzed separately in the assessment. The total Grey Water Footprint of point sources of pollution varied between 1.90 × 1010 and 2.46 × 1010 m3/year. The Grey Water Footprint of domestic pollution represented about ¾ of the total Grey Water Footprint. The Grey Water Footprint of industrial pollution represented about ¼ of the total Grey Water Footprint. The Grey Water Footprint of agricultural point sources of pollution can be neglected on the national level in the Czech Republic. In most cases, the Grey Water Footprint is determined by ammonium nitrogen (NH4-N).