Richard Allan

The water energy food nexus – challenges and emerging solutions

Water, energy and food are the pillars upon which society can further advance. The lack of a secure and economical provision of one of these essentials could result in a breakdown of supply, affordability and accessibility of the two others, especially for the most vulnerable in society. Management of the nexus is of great concern, and the Water Science Forum of the Royal Society of Chemistry have created this brief which outlines some of the challenges and emerging solutions that our members have been focused on.

Drinking water purity – a UK perspective

Water purity is a vague term. Applied to drinking water, the emphasis of pure can mean ‘free from all types of bacteria and viruses’ as defined by the United States Environmental Protection Agency, or as being ‘wholesome’ when defined within Great Britain. US and British standards are based on the protection of public health. Strictly enforced values for a broad set of physical, chemical and biological parameters, informed by expert evidence gathered from many countries over a long period of time, are applied in an effort to ensure a minimum purity is achieved regardless of geographical location within those areas. Other countries like Australia, Canada and New Zealand however, do not have such strict legal definitions. Instead, best endeavours under local circumstances, measured against ‘guideline’ values for a narrow set of parameters, are used to judge water quality, and hence purity. These discrepant definitions can lead to confusion so this brief has been created to clarify current understanding of the meaning of ‘water purity’.

Making Risk Management Stick: Reflections on Risk Governance in Water Utilities

An understanding of the nature and impact of risk within the water sector can only be attained with reference to the societal role which water services play. Although it is not the intention of this contribution to itemise or delineate all relevant risks, a broad overview of the central concerns that drive risk appreciation and management within the sector is warranted. The principal operational driver for any water and wastewater service provider is the delivery of fresh safe drinking water and the removal of waste water in a safe and responsible manner. The Bonn Charter (2004) is the central statement of ambition and constitutes a sectoral commitment setting the framework for the basic operational and institutional arrangements necessary for the provision of water and waste water services, from source to tap.

A risk-based approach for developing standards for irrigation with reclaimed water

A generalised quantitative risk assessment (QRA) is developed to assess the potential harm to human health resulting from irrigation with reclaimed water. The QRA is conducted as a backward calculation starting from a pre-defined acceptable risk level at the receptor point (defined as an annual infection risk of 10-4 for pathogens and by reference doses (RfD) for chemical hazards) and results in an estimate of the corresponding acceptable concentration levels of the given hazards in the effluent. In this way the QRA is designed to inform the level of water treatment required to achieve an acceptable risk level and help establish reclaimed water quality standards. The QRA considers the exposure of human receptors to microbial and chemical hazards in the effluent through various exposure pathways and routes depending on the specific irrigation scenario. By considering multiple pathways and routes, a number of key aspects relevant to estimating human exposure to recycled water can be accounted for, including irrigation and crop handling practices (e.g., non-edible vs edible, spray vs. drip, withholding time) and volumes consumed (directly vs indirectly). The QRA relies on a large number of inputs, many of which were found to be highly uncertain. A possibilistic approach, based on fuzzy set theory, was used to propagate the uncertain input values through the QRA model to estimate the possible range of hazard concentrations that are deemed acceptable/safe for reclaimed water irrigation. Two scenarios were considered: amenity irrigation and irrigation of ready-to-eat food crops, and calculations were carried out for six example hazards (norovirus, Cryptosporidium, cadmium, lead, PCB118 and naphthalene) and using UK-specific input values. The human health risks associated with using reclaimed water for amenity irrigation were overall deemed low, i.e. the calculated acceptable concentration levels for most of the selected hazards were generally far greater than levels typically measured in effluent from wastewater treatment plants; however the predicted acceptable concentration levels for norovirus and Cryptosporidium suggested that disinfection by UV may be required before use. It was found that stricter concentration standards were required for hazards that are more strongly bound to soil and/or are more toxic/infectious. It was also found that measures that reduce the amount of effluent directly ingested by the receptor would significantly reduce the risks (by up to 2 orders of magnitude for the two pathogens). The results for the food crop irrigation scenario showed that stricter concentration standards are required to ensure the effluent is safe to use. For pathogens, the dominant exposure route was found to be ingestion of effluent captured on the surface of the crops indicating that risks could be significantly reduced by restricting irrigation to the non-edible parts of the crop. The results also showed that the exposure to some organic compounds and heavy metals through plant uptake and attached soil particles could be high and possibly pose unacceptable risk to human health. For both scenarios, we show that the predicted acceptable concentration levels are associated with large uncertainty and discuss the implications this has for defining quality standards and how the uncertainty can be reduced.