INCD ECOIND – INTERNATIONAL SYMPOSIUM – SIMI 2016 “THE ENVIRONMENT AND THE INDUSTRY”, PROCEEDINGS BOOK 395 WATER QUALITY INDICES - METHODS FOR EVALUATING THE QUALITY OF DRINKING WATER Iuliana Paun 1 , Liliana Valeria Cruceru 1 , Florentina Laura Chiriac 1 , Marcela Niculescu 1 , Gabriela Geanina Vasile 1 , Nicoleta Mirela Marin 1 1 National Research and Development Institute for Industrial Ecology-ECOIND, 71-73 Drumul Podu Dambovitei, sector 6, Bucharest, 060652, Romania Abstract Water quality is assessed through the biological, physical and chemical parameters. The limits of these parameters that are harmful to human health have been established at national or international level (WHO, EPA, MECC) by various laws, regulations, normative. An efficient and simplified to express the quality of water for consumption is given by the water quality index. It reflects the quality of water in a single value by comparing data obtained from the investigation of a number of physico-chemical and bacteriological parameters with existing limits. This number is placed on a relative scale to justify the quality of water in categories ranging from very poor to excellent. In this study are discussed various water quality indices used to assess the quality of drinking water (surface water). National and international agencies involved in assessing water quality and pollution control defines different quality criteria used for drinking water which is why there are many water quality specific indices for each region or area. In this context, it will present a comparative study of the most important quality indices used to assess water quality worldwide. Keywords: drinking water, surface water, water quality, water quality index 1. Introduction The most important drinking water resurces in the world are the surface water and groundwater. Traditionally, drinking water quality status is professional communicated by comparing the individual parameters (physical, chemical and biological parameters) with guideline values. The limits of those parameters that are harmful to human health have been established at national or international level (WHO, EPA, MECC) by various laws, regulations, normatives. The water quality index aims at assessing the quality of water through a single numerical value, calculated on the basis of one system which convert all the individual parameters and their concentrations, present in a sample into a single value. This is an effective method that allows to compare the quality of various water samples based on a single numerical value and not only the parameters values of each sample. Any result of water quality measurements can serve as indicator of water quality. During the years have been formulated several water quality indices by some national or international organization, which were applied for evaluation of water quality in different particular cases. At global level is not a single index that can describe overall water quality for any water body. However, such a global index of water quality is needed to assess changes in water quality over time and space and also to evaluate successes and failures of international treaties designed to protect aquatic resources. A number of countries have begun the process of developing composite indices of water quality to describe the state of their domestic waters, including the United States of America (Cude 2001), Taiwan (Liou et al. 2004), Argentina (Pesce and Wunderlin