The microbial water quality of therapeutic pools operating without disinfection is recurrently compromised, posing a risk to bathers’ health. The complex composition of such waters and the sensitivity of their therapeutic components hinder the use of traditional chlorine-based disinfectants. The present study aimed to investigate the applicability of a hydrogen peroxide-based disinfectant in therapeutic water in comparison with hypochlorite. Disinfection efficacy, byproduct formation, and the fate of therapeutic components were tested for both disinfectants under laboratory conditions, applying different doses and contact times. Disinfection efficacy was found to be matrix-dependent, especially that of hydrogen peroxide against Pseudomonas aeruginosa (a 10- to 1000-fold difference). Hypochlorite treatment presented a significant chemical risk through the generation of byproducts, mainly brominated and iodinated compounds and combined chlorine. Of the alleged therapeutic components, sulfide ions were eliminated (≥86% loss) by both disinfectants, and hypochlorite reacted with iodide ions as well (≥70% removal). Based on their composition, only 2% of Hungarian therapeutic waters can be treated by chlorination due to high concentrations of ammonia and/or organic compounds. Hydrogen peroxide is applicable to 82% of the waters, as the presence of sulfide ions is the only limiting factor. Due to the matrix effect, close control of residual disinfectant concentration is necessary to ensure microbial safety.

Riverbank filtration is a cost-effective and efficient method for drinking water production, using the natural filtration capacity of the river gravelbed. Removal efficiency for organic micropollutants (OMP) in field studies is generally calculated by comparing the concentrations measured in surface water and in the wells either on the same day or with a shift of fixed time interval, neither of which can account for the variability of surface water quality and travel time in the aquifer. The present study proposes a novel method based on travel time distribution determined by a numerical transport model with a hypothesis that it will provide more reliable estimate for OMP removal. The model was developed for two production sites of Budapest Waterworks, Hungary on Danube River. River water and riverbank filtered well water were sampled regularly for one year (158 samples each) and analysed for 41 OMPs (pesticides, pharmaceutical residues and industrial pollutants). Nineteen pollutants were detected in >50 % of the well water samples. Median removal rates were 4-97 %, while the concentration of five compounds increased in some wells. Removal rates of telmisartan, tramadol, sulfamethoxazole, 4-methyl-benzotriazole, 5-methyl-benzotriazole and desethyl-terbuthylazine correlated negatively to redox potential (|r|=0.456-0.805). Median travel time increased after high flow events resulting in reduced removal of telmisartan, tramadol, 4-methyl-benzotriazole and desethyl-terbuthylazine (|r|= 0.435-0.661). Removal of diatrizoate, iopamidol, tramadol and benzotriazole increased with distance from the shore (148 vs 395 m) by 25 %, 28 %, 8 %, 16 %, respectively. Background groundwater contamination increased pesticide concentration in the wells located in agricultural areas 1.5-5-fold compared to river water. The model-based method gave more consistent results compared to traditional calculations for OMP removal efficiency during the sampling campaign and allowed for estimating the impact of various environmental factors.

Thermal therapeutic pools in most countries are operated in a manner similar to swimming pools: with water circulation, filtration and disinfection. However, in some countries, including Hungary, therapeutic pools are traditionally not treated this way, in order to preserve the therapeutic qualities of the water. However, dilution and frequent water replacement applied in these pools are often insufficient to ensure adequate microbial water quality, posing a risk of infection to the bathers. In the present case study, the impact of water treatment (including chemical disinfection by hypochlorite or hydrogen peroxide) was investigated on the therapeutic components of the water in seven Hungarian spas of various water composition. Microbial quality was improved by both disinfectants, but hypochlorite reduced the concentration of the therapeutic components sulfide, bromide, and iodide ions by 40–99%, and high levels of disinfection by-products were observed. Hydrogen peroxide only affected sulfide ion (91% reduction). Other technological steps (e.g., transport or cooling by dilution) were found to have significant impact on composition, often outweighing the effect of disinfection. The current case study demonstrated that thermal waters may be treated and disinfected with minimal loss of the therapeutic compounds, if an adequate treatment procedure is selected based on the water composition.

Biofilms in drinking water systems hosting diverse microbial communities are potential sources of opportunistic pathogens and taste/odour complaints. Domestic distribution networks are especially prone to biofilm formation due to high surface-to-volume ratio, elevated ambient temperature and intermittent use. Bacterial community diversity and determinants of community structure were investigated in two buildings using a purpose-designed in situ device containing stainless steel and polypropylene coupons and an online biofilm sensor. Next generation sequencing and scanning electron microscopy revealed increasing diversity and complexity over time. Initial biofilms were dominated by Proteobacteria (86–99%, primarily Burkholderiales and Sphingomonadales, core genera Aquabacterium and Blastomonas in month 1, and Rhizobiales in month 3), with an increasing ratio of Actinbacteriota (51–65%, mainly Corynebacteriales) and Bacteroidota (3–5%) by month 6. The impact of the sampling location was secondary to biofilm age in determining microbial diversity, and within-building variation was comparable to differences between facilities. The coupon material had a negligible effect on community structure. Real-time monitoring by online sensors did not yield interpretable data. Important nosocomial pathogens (Mycobacterium, Legionella, Methylobacterium, Bosea) were detected in the biofilm samples that were absent in bulk water, implying that water monitoring alone is not sufficient for estimating the risk of water-related pathogens.