January 2021

ASSESSING GROUNDWATER QUALITY: A GLOBAL PERSPECTIVE

Summary

This perspective paper by the Friends of Groundwater (FoG) group aims to give a compelling argument for the importance of groundwater quality for human development and ecosystem health. It also provides a global overview of the current knowledge, with focus on data coverage, gaps and technological advances. It is a building block towards a future global assessment of groundwater quality as part of the United Nations Environment Programme (UNEP) World Water Quality Assessment (WWQA).

Groundwater is an essential global resource and provides the largest store of freshwater, apart from the ice caps. Current groundwater abstraction represents 26% of total freshwater withdrawal globally, to supply almost half of all drinking water and 43% of the consumptive use in irrigation. In arid and semiarid regions, groundwater is the only reliable water resource. In the environment, groundwater makes an important contribution to river flow and groundwater dependent ecosystems.

For drinking water supply, one of the advantages of groundwater is that it is naturally protected from many contaminants. With drought and climate change, people in water-scarce areas will increasingly depend on groundwater, because of its buffer capacity and resilience to rapid impacts. However, groundwater quality, as well as quantity, may be impacted by climate change.

A global groundwater quality assessment is needed because human activities and climate variability increase the pressure on groundwater resources, but it is an invisible resource that remains out of sight and out of mind for most people. Protection of our groundwater resources is necessary for protecting human health, maintaining food supplies and conserving ecosystems. Many regions and countries rely on naturally clean groundwater as advanced water treatment is economically infeasible. Knowing where to source clean groundwater, as well as understanding threats to this resource, is therefore important.

The principal objectives of this perspective paper are to present the importance of groundwater to meet the Sustainable Development Goals (SDGs), notably SDG3, SDG6 and SDG7, describe the threats to groundwater quality from anthropogenic and geogenic contaminants, discuss the challenges of providing a global overview of groundwater quality, present key messages to summarise current knowledge and capacity and outline a Work Plan to develop a global groundwater quality assessment network, including protection and management of groundwater quality.

The key messages from this perspective paper are that:

  1. Increased attention to water, and specifically groundwater quality, is of utmost importance forthe achievement of the Sustainable Development Goals, especially related to water security (SDG6), health (SDG 3), and food production (SDG 2). Groundwater quality is under increasing pressure due to human development and the impacts of climate change posing risk to human consumption and affecting to a large extent disadvantaged vulnerable groups in society.
  2. A dedicated global groundwater quality assessment is necessary and timely. It will provide a comprehensive and coordinated overview of the knowledge base pertaining to groundwater quality, including mapping of main drivers, pressures, trends and impacts, as well as current and prospective management approaches.
  3. There is a large variety of anthropogenic and natural (geogenic) chemical and microbiological contaminants that are found or move into aquifers across the globe. The range of characteristics and behaviour in the groundwater systems requires expert knowledge.
  4. Groundwater systems are heterogeneous, three-dimensional water reservoirs in porous and fractured rock formations. Groundwater contaminant distributions are therefore particularly challenging to map. Also, contaminant transport and remediation of pollution in these systems often involves long timescales. Hence, groundwater quality is more complex to understand, assess and remediate than surface water quality.
  5. Information and data on groundwater quality are very variable across the globe, with often less information available in countries of the Global South. For a comparable global assessment, substantial efforts are needed to i. Improve data collection, ii. Develop the capacity and the knowledge base, with particular focus on developing countries and iii. Develop international standards.
  6. Groundwater quality needs to be understood at various scales depending on the key risks, e.g. related to the size and vulnerability of the aquifers and receiving water bodies, the inherent or external pollution loads, land use, waste handling, and the demand on the resource. There is a need to consider groundwater quality for different uses: e.g. drinking water, ecosystems, food (particularly irrigation), energy production and other industries.
  7. Groundwater monitoring programmes need to be targeted and designed according to the purpose of the monitoring, e.g. specific contamination tracing and remediation, short-term campaigns to understand local contamination issues, and longer-term larger-scale systematic monitoring programmes to identify general spatial patterns and long-term temporal trends in groundwater quality.
  8. Besides traditional groundwater monitoring programmes involving water sampling in wells (points in space), upstream (soils), and downstream (receiving streams, springs, wetlands and coastal areas) need to be considered. Important new technologies and practices are developing, e.g. earth observations and GIS, Citizen Science, machine learning, and numerical modelling of contaminant fate and transport. Due to general lack of in-situ data, the new technologies can help extrapolate knowledge from regions with good data to areas with less information, giving an understanding of potential risks and vulnerabilities. Vulnerability and pollution load mapping are critical factors in tracing potential groundwater pollution and designing monitoring programmes on groundwater quality.
  9. Most monitoring programmes for groundwater quality are based on national level legislation and regulations, where these exist. Special attention is required for groundwater quality challenges in transboundary aquifers. To fill knowledge gaps and prepare an improved and fair basis for transboundary cooperation requires development of comparable standards for the aquifers, data sharing and joint capacity development programmes.
  10. Local-to-global partnerships and investments in research, capacity development and evidencebased policymaking are required to make the step change required to manage groundwater quality sustainably.

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