waddington points out that while water supply interventions appear ineffective averaging a negligible and insignificant impact on diarrhoea morbidity compared to controls water quality interventions on average lead to a relative reduction in child diarrhoea morbidity with a confidence interval such authors argue that treatment at point of use is more efficient than treatment at the point of source via a community water treatment plant for example given that there are many opportunities for treated water to become unsafe alongside the transportation process waddington wright et al these interventions can include ceramic water purifiers sodis sand biofilters etc an example of efficient water treatment interventions at household level is described in box only certain areas are affected by high arsenic levels but tens of thousands of people have already been showing skin discoloration and other more serious manifestation of chronic poisoning including neurologic vascular and carcinogenic effects water quality interventions conducted over longer periods tend to show smaller effectiveness while impact appears to fall markedly over time