Abstract:
A frequent complaint of the inhabitants (primarily, farmers) of Polpithigama Divisional Secretariat in
Kurunegala District, is the increasing hardness in dug wells and tube wells and as a result new wells
are dug in search of water without hardness. Besides, a chronic kidney disease has been rapidly
spreading among people within the last decade.
A preliminary study was carried out to determine the ground water quality of the study area using
dug-wells located in Mahawa, Siyambalangamuwa area. Sampling wells were chosen across an
elevation gradient that extends from hills towards the paddy fields. Samples were taken from the
surface of water and from the bottom of the well. Samples of groundwater in triplicate were collected
into polypropylene bottles (rinsed with 10% nitric acid, followed by de-ionized water) from dug wells
used by the villagers for drinking and domestic use. Immediately after measuring the pH of the water
samples, 1 ml of concentrated HNO3 (0.1% v/v) was added to the sample bottle for preservation and
they were brought to the laboratory. Calcium hardness, total hardness (Ca2+ and Mg2+) and other ions
(PO4
3-,SO4
2-,NO3
-,CO3
2-) in water samples were measured. Ca2+ and total hardness were measured
using EDTA titration. PO4
3-,SO4
2-,NO3
- contents were measured colorimetrically using
spectrophotometer. An acid titration was used to determine the CO3
2-.
Total hardness (as CaCO3) of water (n=20) ranged 150-420 ppm and Ca2+ hardness ranged 110–390
ppm. PO4
3- and SO4
2- contents of the samples ranged between 1 - 22.4 ppm and 12.5–605 ppm
respectively. CO3
2- was ranged 24-492 ppm and NO3
- was ranged 1 – 6 ppm. Hardness of bottom
layer of water in the wells was significantly higher than that of the surface water samples. These
levels exceed WHO prescribed values for drinking water. Results substantiate the general complaint
by the villagers in the study area that the quality of water is unacceptable for drinking. A potential
cause of increasing groundwater hardness may be due to accumulating ions in the water from
increasing amounts of inorganic ions leached into groundwater from agrochemicals used abundantly
in this area.
