The study was conducted in Poland and in a coastal region of Spain (Castilla-La Mancha, Murcia, and Comunidad Valenciana) and aimed to collect and compare data on the quantity and composition of backwash water generated during the rinsing of sand, silica, and carbon bed filters, as well as the methods of its management at selected drinking water treatment plants (WTPs). The analysis was based on survey responses from 66 Polish and 6 Spanish water utilities. Most Polish responses lacked data on the composition of backwash water, as such analyses are not routinely carried out. Polish WTPs typically have capacities up to 100,000 m 3 /day, while Spanish facilities range from 69,100 to 458,000 m 3 /day. These differences reflect the varying water supply systems in both countries—Polish plants supply individual towns, whereas Spanish plants operate within centralized, regional networks. The results indicate that backwash water has the potential to serve as an additional water source but requires regular monitoring of both quantity and composition, which is currently uncommon. Legal regulations governing backwash water reuse are needed to ensure its safe and efficient application. In Poland, increasing the share of managed backwash water is particularly important. It was also found that returning small volumes of untreated backwash water to the treatment process does not compromise the quality of the final treated water. These findings highlight the need for improved regulatory, operational, and monitoring frameworks to support sustainable water management practices.
Wolska et al. (Sun,) studied this question.