Chennai is the largest city in South India located in the eastern coastal plains. Water supply to the Chennai city is met by reservoirs and by groundwater. Most of the groundwater is pumped to the city from the well fields located in the Araniyar and Korttalaiyar River (A-K River) catchment north of Chennai.

The EU-funded R&D project DEMEAU addresses the fate of emerging pollutants in water and waste water treatment, e.g. Managed Aquifer Recharge (MAR). For MAR the objectives are to mobilize existing experience from different European study sites and to develop a systematic approach for the authorization of new recharge schemes in compliance with the European water and groundwater directives. The activities will cover the issue of infiltrating and injecting treated wastewater as well as developing guidance on optimum design and operation of infiltration facilities. In order to demonstrate the effects of typical existing European MAR systems onto groundwater availability and groundwater quality with specific focus on trace organics, a comprehensive relational database (catalogue) on European MAR systems was created to ensure efficient management of available data. By means of the built-in user forms, queries, and reports, database users are enabled to not only view and enter records but also to quickly process the data to extract needed information. In total, 59 different parameters were selected in order to describe about 270 documented MAR sites in 23 countries in Europe. These parameters were then divided up into four main groups (general information, technical data, hydrogeological parameters and monitoring activities) plus references. The database was created using standard software (MS ACCESS) and references were managed by open source software (JABREF). The compiled data on European MAR sites was taken from a variety of different source types, including scientific articles, books, PhD, diploma and master's theses, presentations, technical documents, reports from previous national and EU research projects, personal communication with specialists, operators and water authorities, community and operator websites, newspaper articles, and Google Earth (for geographic coordinates to create overview maps). On the basis of this database a classification system for the MAR sites found in Europe will be developed that can be used for deriving site-specific pre-requisites and design criteria as guidance for the authorization of for new sites.

Groundwater exploitation in India has increased rapidly over the last 50 years as reflected by the growth of the number of groundwater abstraction structures (from 3.9 million in 1951 to 18.5 million in 1990) and shallow tube wells (from 3000 in 1951 to 8.5 million in 1990) (Muralidharan, 1998; Singh & Singh, 2002).Today groundwater is the source for more than 85 % of India’s rural domestic water requirements, 50 % of urban water and more than 50 % of irrigation demand. The increase in demand in the last 50 years has led to declining water tables in many parts of the country. For example, 15% of the assessment units (Blocks/Mandals/Talukas) have groundwater extraction in excess of the net annual recharge (Central Ground Water Board, 2007). According to Rodell et al. (2009), the extent of groundwater depletion between 2002 and 2008 was 109 km3, which is about half the capacity of India’s total surface-water reservoirs.

Chennai is the largest city in South India located in the eastern coastal plains. Water supply to the Chennai city is met by reservoirs and by groundwater. Most of the groundwater is pumped to the city from the well fields located in the Araniyar and Korttalaiyar River (A-K River) catchment north of Chennai.

It was the aim of the EU funded research project TECHNEAU to investigate the relevance and feasibility of bank filtration (BF) plus post-treatment for newly industrialised and developing countries. Field studies at BF sites in Delhi (India) were supplemented by literature studies and modelling in order to investigate if this natural drinking water (pre-) treatment is a sustainable option to provide safe drinking water for countries like India. The results showed that especially for those substances that are of relevance in newly industrialised and developing countries subsurface passage can represent an efficient barrier. However, certain limiting factors for BF application also need to be considered: high ammonium levels in surface water, usually associated with high shares of poorly or un-treated sewage, will not be mitigated during subsurface passage and require extensive post-treatment. In order to support decision makers in the difficult task of assessing the feasibility of BF systems at a certain site a simple decision support system was developed. This simple tool enables to assess a range of abstraction rates and well locations for a specific field site that could fit with their needs (e.g. minimum required travel time or share of BF).

Bank filtration (BF) is a well established and proven natural water treatment technology, where surface water is infiltrated to an aquifer through river or lake banks. Improvement of water quality is achieved by a series of chemical, biological and physical processes during subsurface passage. This paper aims at identifying climate sensitive factors affecting bank filtration performance and assesses their relevance based on hypothetical 'drought' and 'flood' climate scenarios. The climate sensitive factors influencing water quantity and quality also have influence on substance removal parameters such as redox conditions and travel time. Droughts are found to promote anaerobic conditions during bank filtration passage, while flood events can drastically shorten travel time and cause breakthrough of pathogens, metals, suspended solids, DOC and organic micropollutants. The study revealed that only BF systems comprising an oxic to anoxic redox sequence ensure maximum removal efficiency. The storage capacity of the banks and availability of two source waters renders BF for drinking water supply less vulnerable than surface water or groundwater abstraction alone. Overall, BF is vulnerable to climate change although anthropogenic impacts are at least as important.

In the densely populated semi-arid territory around Delhi, the water demand is rising continuously, while the surface- and groundwater resources are threatened by contamination and overexploitation. This is a typical scenario in many newly industrialising and developing countries, where new approaches for a responsible resources management have to be found. Bank filtration holds a great potential, thus being a low tech method and benefiting from the storage and contaminant attenuation capacity of the natural soil/rock. For this study, three field sites have been constructed to investigate bank filtration in different environments in and around the megacity with a main focus on inorganic contaminants. Hydraulic heads, temperature gradients and hydrochemistry of surface water and groundwater were analysed in three different seasons. Depending on sitespecific conditions, distinct hydrogeological conditions were observed and both positive and negative effects on water quality were identified. Most concerning issues are the impact of anthropogenic ammonia, the mixing with ambient saline groundwater and the mobilisation of arsenic during the reductive dissolution of manganese- and iron(hydr)oxides. Positive aspects are the dilution of contaminants during the mixing of waters from different sources, the sorption of arsenic, denitrification, and the precipitation of fluoride under favourable conditions.

Submersible data loggers are widely used for groundwater monitoring, but their application often runs the risk of hardware and data loss through vandalism or theft. During a field study in India, the authors of this article experienced that well locks attract the attention of unauthorized persons and do not provide secure protection in unattended areas. To minimize the risk of losing data loggers, a cheap and simple solution has been invented to hide the instruments and associated attachments below the ground surface, inside observation wells. It relies on attaching the logger to a length of small-diameter pipe that is submerged at the bottom of the well, instead of attaching it to the top of the well. The small-diameter pipe with the logger is connected to a small bottle containing a magnet that floats on the water surface of the well and can be recovered using another bottle also with a magnet. A logger that is concealed in this way is difficult to detect and access without knowledge of the method and adequate removal tools. The system was tested and successfully applied for monitoring shallow

The use of bank filtration for drinking water treatment in Europe dates back to the days of beginning industrialization in the 19th century. With regard to improved source water quality in Europe, the millennium development goals and global climate change, aquifer recharge (AR) and bank filtration (BF) need to be reassessed in terms of sustainability and their role within an integrated water resource management. Based on the IC-NASRI study comprising 194 drinking water facilities worldwide integrating aquifer recharge techniques in their treatment system, an average AR/BF site would be located in Central Europe alongside a river and is characterized by: a sandy gravel aquifer with a hydraulic conductivity of 2x10-3 m/s, a maximum aquifer thickness of 30 m, 175 m travel distance from bank to well, a travel time of 70 days and by vertical well operation with a daily capacity of 55.000 m³. A literature survey conducted within the TECHNEAU project demonstrated that for substances highly relevant to newly-industrialized or developing countries (e.g. pathogens) the removal efficiency is good. Hydro-chemical analyses from three study sites in Delhi support these results. However, it was also shown that poor surface water quality, saline groundwater or subsurface conditions leading to mobilization of trace metals like iron, manganese or arsenic may limit the applicability of AR / BF without further post-treatment. Climate change might affect the performance of AR / BF worldwide, impairing source water quality and influencing removal efficiency. However, other factors like changes in demography or land-use can impact the systems by far more severely.