Fate and behaviour of microplastics (>25µm) within the water distribution network, from water treatment works to service reservoirs and customer taps

Water treatment works have previously shown high efficiency in removing microplastics > 25 µm from raw source water. However, what is less well known is the extent to which microplastics of this size class are generated or lost within the water distribution network, particularly whether there is a greater presence in the customer tap than in the water treatment works outlet. This study focused on the presence of 21 different types of synthetic polymer particles with sizes larger than 25 µm examined through multiple rounds of sampling at outlets of water treatment works (WTW), service reservoirs (SR), and customer taps (CT) managed by seven different water companies in Britain. Nineteen different types of polymers were detected; their signature and concentration varied based on the round of sampling, the location within the water supply network, and the water company responsible for managing the supply. Among the polymers examined, polyamide (PA), polyethene terephthalate (PET), polypropylene (PP), and polystyrene (PS) were the most commonly found. Apart from PET having its highest concentration of 0.0189 microplastic per litre (MP/L) in the SR, the concentrations of the other three most frequent polymers (PS = 0.017 MP/L, PA = 0.0752 MP/L, PP= 0.1513 MP/L) were highest in the CT. The overall prevalence of this size of microplastics in the network is low, but there was a high variability of polymer types and occurrences. These spatial and temporal variations suggested that the MP in the distribution network may exist as a series of pulses. Given the presence and polymer types, the potential for some of the microplastics to originate from materials used in the water network and domestic plumbing systems cannot be ruled out. As found before, the absolute number of microplastics in the water distribution network remained extremely low.