INTRODUCTION

Fresh water quality, has gained substantial attention in recent years throughout the world (Chang 2004). Groundwater (0.06% of Earth’s available water) is a key source of drinking water among freshwater resources. This relatively small volume is critically important as it represents 98% of the freshwater readily available to humans (Zaporozec and Miller 2000). India, diverse in terms of population (70% rural and 30 % urban) depends on groundwater for drinking and domestic purposes (Jaiswal et al. 2003; Reddy et al. 1996). Groundwater meets the drinking water requirement of over 50% of Kerala’s population (Kerala Water Authority 1991; Pillai and Ouseph 2000; Roy 2004).

The physico-chemical and biological characteristics of groundwater in a given area is determined by the natural - geological formations (Subramani et al. 2005), weathering, dissolution, precipitation, ion exchange and biological processes (Jeevanandam et al. 2007) as well as anthropogenic activities. Often groundwater is being contaminated by non-point sources (agricultural, urban runoff) and by point sources (sewage, industrial effluents disposal) in many developing countries including India (Jain et al. 2010; Jeevanandam 2007). In recent years, the unplanned urbanization has influenced the quality as well as quantity of the water, evident from declining groundwater table, higher levels of contamination (Ramachandra and Uttam Kumar 2008). These factors have necessitated the understanding of groundwater quality in recent years (Yanggen and Born 1990).

In Kerala, prevalence of water borne diseases like diseases of gastro-intestinal system (Panikar and Soman 1984), diarrhea, dysentery, typhoid, worm infestations and infectious hepatitis (Aravindan 1989; Kunhikannan and Aravindan 2000) are attributed to groundwater contamination, especially faecal coliform contamination (Babu et al. 2007; Calvert and Andersson 2000; Harikumar and Kokkal 2009; Kerala Water Authority 1991; Laluraj et al. 2005; Laluraj et al. 2006; Panicker et al. 2000; Radhakrishnan et al. 1996; Rahiman et al. 2003; Rejith et al. 2009; Varghese and Jaya 2009). Low pH was reported from many places (Gopinath and Seralathan 2006; Harikumar and Kokkal 2009; Laluraj and Gopinath 2006; Rejith et al. 2009; Vijith and Satheesh 2007). HariKumar and Kokkal (2009) have also reported the high amount of alkalinity, magnesium, hardness, chloride, calcium and TDS. The contamination of groundwater by chloride, TDS and fluoride have been reported by George and Prakasam (2008), Harikumar et al. (2000), Laluraj et al. (2005) and Shaji et al. (2007, 2009).

Most of these reports are fragmented and were restricted to a particular panchayat or river basin or district.  A comprehensive study covering the entire region would aid the decision making process to implement an effective strategies to minimize or mitigate contamination of drinking water sources. This study focuses the physico-chemical and biological quality of groundwater throughout Kerala to assess its suitability for drinking as per standards (Bureau of Indian Standards -BIS 1991) and to see the types of hydrochemicals and spatial distribution of major ions.