Ground water is a vital source of fresh water in
both urban and rural regions of the world. In Kerala,
ground water meets the drinking needs of more than 60%
population. Thrissur is the central district of Kerala, with
a special well culture. Mostly each and every home has a
dug well and ground water is the major source of drinking
water in the district. Hence it is necessary to evaluate the
ground water quality of Thrissur to ensure safe drinking
water. Water quality index evaluation is an essential step to
monitor, control and prevent the ground water pollution.
The water quality index calculated for 56 observation wells
of study area indicates the suitability of drinking water in
each well. However there exist some uncertainties in the
conventional method of water quality index evaluation.
Fuzzy logic implemented in water quality index evaluation
makes it more reliable in conveying the accurate status of
ground water quality. Mamdani fuzzy inference system
model with 10 inputs and single output was created for
index evaluation. Trapezoidal membership function plots
were assigned for both inputs and output and a total of 412
possible rules were created based on the water quality data
and water quality standards. Fuzzy index reveals that 70%
of drinking water in the study area belongs to excellent
category, 16% belongs to good category and remaining
14% belongs to poor category that is unfit for drinking.
According to fuzzy index Kodungallur, Keechery and
Azhikode were the major ground water contamination sites
identified in the study area. Relative root mean square
error value of 1.2 % was obtained by comparing both index
values. From the year 2015 to 2019 the percentage of poor
water category has changed from 6% to 14% which
indicates an increasing ground water contamination issue
that needs immediate attention.