PURPOSE: To obtain alkali water without using a power source by housing a filter packed with the solid basic substance contg. Mg or MgO into a retention vessel in providing the clearances.

CONSTITUTION: A filter 7 packed with the solid basic substance 6 contg. Mg or MgO is housed into a retention vessel 8 in providing the clearances. By this constitution, alkali water can be obtained without using a power source. There is no dirt in water and the elevation of pH is maximumly reached to 10 and water can be made to weak alkalinity. Furthermore since the chemical reaction is mild, the daily dissolving quantity of Mg or MgO is remarkably slight and it can be used for a long period and the formation of residue such as magnesium hydroxide is little and the handling is easy.