The slight increase in the pH of water passed through the ceramic filters is due to the presence of the mineral Wollastonite in the ceramic water filter. Wollastonite is slightly soluble and alkaline, so may partly dissolve in the water as it passes through the filter causing a minor pH shift which is harmless. No health based guideline value for pH in drinking water has been proposed by the WHO, although accompanying notes to the guidelines state that the pH range is often in the range of 6.5-9.5. In general there is little evidence to suggest that pH in potable water of around 9-10 is of public health significance.