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Top1. Introduction
Health is critically dependent on the quality of drinking water (Chowdhury et al., 2019; Clasen et al., 2014; Daughton, 2018; Koopaei and Abdollah, 2017), but many health care professionals tend to somewhat reduce its significance to maintaining physiological functions, e.g., blood pressure, pH, and body temperature (Armstrong and Johnson, 2018; Perrier, 2019). Yet, throughout recorded human history the preventive and curative power of water was well known and part of various therapeutic approaches (Moss, 2010). Even if one disregards or questions the healing properties of water, many entertain a widespread misconception with regard to the quality of drinking water. The rapidly rising number of toxic substances contaminating municipal surface and groundwater impacts all wastewater treatment works (Petrie et al, 2015). Flowing waters used as municipal water supplies also show high concentrations of contaminants which act as vectors for waterborne contaminants or pathogens (Lechner, 2020). However, there is a discrepancy in the understanding of the situation and its implication for public health. A recent American survey of perceptions about water showed that while 60 percent of the experts recognized that pathogens, fertilizers or pesticides pose a risk to public water systems in the U.S., the majority still rated the water supply as normal or good (Eck et al., 2019). This contradiction could stem from a subjective probability bias or a defense mechanism (Ferrer and Klein, 2015), which is even more accentuated if one takes into account additional factors that may corrupt tap water quality. Apart from microbiological and biochemical concerns, water treatment and transportation are additional potential harmful factors. It has been argued that the intake of ‘stressed’ water disrupts the water between and within cells in the human body and may prompt pathological macromolecular changes (Davidson et al., 2013). Among such stressors are, e.g., water disinfection (e.g. chlorine or ozone), supplementation (e.g. fluoride), and compression of water through pipe transportation from the supplier to the household. Bottled water, which some regard as a viable alternative, is also contaminated, regardless of whether the bottle is made of plastic or glass. For instance, in a recent study testing 259 bottles from 19 different countries, 93 per cent showed some sign of microplastic contamination (fragments and fibers), which stemmed from both packaging and bottling (Mason et al., 2018). In a large study conducted in Germany, the country with the highest number of bottled mineral water brands, about one third failed to meet the drinking water regulations defined by the EU (Birke et al., 2010). A recent systematic review selecting studies that used procedural blank samples and a validated method for particle composition analysis found that the high-quality studies confirmed strong microplastic contamination of drinking water with the maximum reported contamination of 628 MPs/L for tap water and 4889 MPs/L for bottled water (Danopoulos et al., 2020).