CECs demonstrated variable stability in UK river water over 24 hour storage. A full breakdown of results may be found in the supplementary information (table ). In general CECs from group A demonstrated better overall stability in comparison to group B (overall averages, 0 ± 21% vs -2 ± 41% degradation respectively). In group A, good stabilities were observed for all CECs studied from the beta-blockers and antiepileptic classes (-7 ± 4%). Regarding group B, whilst good stabilities were observed for AAs, including sulfamethoxazole, sulfapyridine and trimethoprim (5 ± 3%). Poorer stability was observed for methyl paraben and ofloxacin (figure ). Ofloxacin observed ~50% degradation in river water over 24-hours, yet minimal degradation was observed for 24-hour stability study on cartridge (~12%). Similar results for the antiviral, emtricitabine, were also observed, with ~50% degradation in river water but only observing ~-20% on cartridge.