Water quality evaluation by index in Dalmatia

This article describes the process of determining the water quality index (WQI) for Dalmatian County waters as well as the results of the application of the index for water evaluation in Dalmatia (Southern Croatia) for a three year period (1995, 1996; 1997). WQI includes the following nine parameters: temperature, mineralization, corrosion coefficient, K = (Cl + SO4)/HCO3, dissolved oxygen, biochemical oxygen demand, total nitrogen, protein N, total phosphorus and total coliform bacteria (MPN coli/100 ml) for which concentrations C-80 are calculated. After completing the nine parameters the results of C80 were recorded and transferred to the score table to obtain the q-value. The q-value used is an attempt to quantify environmental factors which would otherwise be qualitative. For each parameter the q-value was multiplied by a weighting factor based upon the relative significance of the parameter. The nine resulting Values were then added to arrive at an overall WQI. The WQI is obtained so that the water quality evaluation (WQE) can be divided by water quality evaluation (WQE)(MAC) which satisfies the maximum admissible concentration (MAC) of first class water. It includes both underground and surface water, which can be used in its natural state or after being disinfected for drinking water. Spring and river waters in Dalmatia which contain low sulphate and chloride concentrations are of high sanitary quality. This duality can be estimated by the WQI (quality index), which varies around 1. The increase of sulphate as well as chloride in springs, rivers and underground waters decreases the WQI value; in fact, it causes deterioration of the water quality according to the established standard for drinking water. (C) 1999 Elsevier Science Ltd. All rights reserved.