In 2020, the European Union published ordinance EU 2020/741, establishing minimum requirements for water reuse in agriculture. The ordinance differentiates between several water quality classes. For the highest water quality class (Class A), the ordinance mandates analytical validation of the treatment performance of new water reuse treatment plants (WRTP) related to the removal of microbial indicators for viral, bacterial, and parasitic pathogens. While the ordinance clearly defines the numeric target values for the required log10-reduction values (LRV), it provides limited to no guidance on the necessary sample sizes and statistical evaluation approaches. The main requirement is that at least 90 % of the validation samples should meet the requirements. However, the interpretation of this 90 % validation target can significantly impact the required sample size, efforts necessary, and the risk of misclassifying WRTPs in practice. The present study compares different statistical evaluation approaches that might be considered applicable for LRV validation monitoring. Special emphasis is placed on the use of tolerance intervals, which combine percentile estimations with sample size-based uncertainty and confidence regions. Tolerance interval-based approaches are compared with alternative methods, including a) a binomial evaluation and b) the calculation of empirical percentiles. The latter are already used in existing European and U.S. regulations for bathing water and irrigation water quality.

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.

In the course of identifying areas of relevance for further research and development the members of the European Water Supply and Sanitation Technology (WssTP) identified Managed Aquifer Recharge (MAR) as an important cross-cutting topic and area relevant for further research. For this reason a Task Force on MAR was initiated with 36 representatives from European research institutes and industry partners with participation of international experts. These task force members developed the basis for a report documenting the state of the art and research needs in the field of MAR that has now been published by the WssTP.