One of chemical requirement for drinking water is hardness. Water with high level hardness is
very dangerous for human health, specifically for kidneys. MPN coliform as one of bacteriological
requirements for water quality is an indicator for excreta pollution. The aim of the study was to
decrease water hardness and coliform in water wells of Jimbung Villages in Kalikotes, Klaten by
installing ZeRAK filter, which consists of zeolite, resin, chlorine and activated charcoal. The study
was an experiment with pre-test and post-test design. As a study sample were 45 wells that were
connected with plumbing in that village. The results show that before the filtration, the average of
water hardness was 270 mg/l, while post-filtration it was 44 mg/l (84%). Coliform pre-filtration
were in a range between 111 and 1898 MPN per 100 ml, and after treatment they were between
0 and 7 MPN. Statistically, the differences are significant (both p-values <0,001). To conclude,
ZeRAK filter used in this study is effective to decrease water hardness and coliform.