I don’t know much about it, but here in France the government has published some info. normandie.fr/fileadmin/mediatheque/Fiches_Etudes/fiches/aep/01aep11.htm To summarize: Nickel is poorly eliminated in the treatment of drinking water because it requires pH levels above 9.5. The most common ways of removing nickel involve physico-chemical methods such as coagulation and active carbon adsorption as well as membrane filtration. However, there are conflicting studies about how effective these processes actually are. Manganese dioxide (MnO 2), however, does seem to be promising and can be used on an industrial scale. It requires pH greater than 7. Filtration using manganese dioxide has already been approved.