Groundwater Assessment Platform (GAP)

Groundwater quality information management system on geogenic contaminants

The Groundwater Assessment Platform (GAP) is an SDC-supported project to develop an online GIS-based data and information portal for groundwater-related questions, with a special focus on the geogenic contaminants arsenic and fluoride.  These naturally occurring groundwater pollutants affect 100’s of millions of people worldwide with minor to severe health problems. provides state-of the-art global arsenic and fluoride contamination risk maps and enables users to upload and map their data as well as to create their own groundwater quality models. In the GAP Wiki, users can share documents as well as discuss relevant issues in an open setting. GAP follows upon the Water Resource Quality (WRQ) project, which dealt with the mitigation of geogenic groundwater contamination and published the Geogenic Contamination Handbook.

Geogenic Contamination

Geogenic contamination refers to naturally occurring elevated concentrations of certain elements in groundwater (such as arsenic, fluoride, uranium, manganese or selenium) that have a negative health effect on humans consuming this water. Geogenic contamination of groundwater might be a result of geochemical characteristics of the aquifer material – e.g. high concentrations of the contaminant in the rock matrix, dissolving during water-rock interaction, or occur due to environmental conditions such as an arid climate or reducing conditions in the aquifer which facilitate the contaminant to occur in a more mobile state.

The most wide-spread geogenic contaminants are arsenic and fluoride, affecting the health of hundreds of millions of people worldwide.


Fluoride is the 13th most abundant element in the earth’s crust (625 mg/kg) and exists in trace amounts in almost all groundwaters across the world. According to estimations from UNESCO, more than 200 million people worldwide rely on drinking water with fluoride concentrations exceeding the present WHO guideline of 1.5 mg/L. Fluorosis, associated with elevated fluoride concentrations in drinking water has been reported in a range of countries.

While low fluoride intake may prevent dental caries, excess intake causes different types of fluorosis; primarily dental and skeletal fluorosis. White line striations on the teeth followed by brown patches and, in severe cases, brittling of the enamel are common symptoms of dental fluorosis. This is not only a health problem but also has psychological and social impacts, as people are ashamed and possibly ostracised due to their bad teeth. Skeletal fluorosis first causes pain in different joints, then limits joint movement, leading to stiffness and skeletal crippling. Besides dental and skeletal fluorosis, other manifestations such as nervousness, depression and muscle weakness have been reported in connection with high fluoride intake.

More information:

Water Quality Section of the Catholic Diocese of Nakuru, Kenya

International Society for Fluoride Research

WHO: Fluoride in Drinking Water


The WHO guideline value for arsenic in drinking water has been set to 10 µg/L, though in several countries higher values are used (e.g. 50 µg/L in China).

High arsenic concentrations in groundwater have been found to be responsible for health problems summarized under the term arsenicosis, which develop over a period of several years. Symptoms of arsenicosis range from skin disorders (melanosis, keratosis) to cardiovascular diseases, cancer and the impairment of the neurodevelopment of children. Since there is no cure for arsenicosis to date, the provision of safe water for the prevention of this disease is the vital mitigation approach.

More information:

WHO: Arsenic in Drinking Water


The GAP team comprises geoscientists, modellers and programmers from the Eawag departments of: Water Resources and Drinking Water (W+T) and Water and Sanitation in Developing Countries (SANDEC) as well as the firms Ernst Basler and Partner and  Hydrosolutions Ltd.

GAP Team

Prof. Dr. Michael BergHead of DepartmentTel. +41 58 765 5078Send Mail

Project Manager


Dr. Joel PodgorskiTel. +41 58 765 5760Send Mail

Project Coordinator

Dr. Tobias Siegfried
Tel. +41 44 586 01 52

Business planning

Jakob Steiner
Tel. +41 76 44 88 346

Website development

Water and waste(water) Management


The GAP team is involved in collaborative projects with researchers in Brazil, Burkina Faso, Ethiopia, India, Pakistan and Peru.


Podgorski, J.; Berg, M. (2020) Global threat of arsenic in groundwater, Science, 368(6493), 845-850, doi:10.1126/science.aba1510, Institutional Repository
Wallis, I.; Prommer, H.; Berg, M.; Siade, A. J.; Sun, J.; Kipfer, R. (2020) The river-groundwater interface as a hotspot for arsenic release, Nature Geoscience, 13, 288-295, doi:10.1038/s41561-020-0557-6, Institutional Repository
Stopelli, E.; Duyen, V. T.; Mai, T. T.; Trang, P. T. K.; Viet, P. H.; Lightfoot, A.; Kipfer, R.; Schneider, M.; Eiche, E.; Kontny, A.; Neumann, T.; Glodowska, M.; Patzner, M.; Kappler, A.; Kleindienst, S.; Rathi, B.; Cirpka, O.; Bostick, B.; Prommer, H.; Winkel, L. H. E.; Berg, M. (2020) Spatial and temporal evolution of groundwater arsenic contamination in the Red River delta, Vietnam: interplay of mobilisation and retardation processes, Science of the Total Environment, 717, 137143 (13 pp.), doi:10.1016/j.scitotenv.2020.137143, Institutional Repository
Podgorski, J.; Berg, M.; Kipfer, R. (2019) Isotope mapping of groundwater pollution and renewal, IAEA Bulletin, 60(1), 31-32, Institutional Repository
Podgorski, J. E.; Labhasetwar, P.; Saha, D.; Berg, M. (2018) Prediction modeling and mapping of groundwater fluoride contamination throughout India, Environmental Science and Technology, 52(17), 9889-9898, doi:10.1021/acs.est.8b01679, Institutional Repository
Razanamahandry, L. C.; Andrianisa, H. A.; Karoui, H.; Podgorski, J.; Yacouba, H. (2018) Prediction model for cyanide soil pollution in artisanal gold mining area by using logistic regression, Catena, 162, 40-50, doi:10.1016/j.catena.2017.11.018, Institutional Repository
Bretzler, A.; Stolze, L.; Nikiema, J.; Lalanne, F.; Ghadiri, E.; Brennwald, M. S.; Rolle, M.; Schirmer, M. (2018) Hydrogeochemical and multi-tracer investigations of arsenic-affected aquifers in semi-arid West Africa, Geoscience Frontiers, 10(5), 1685-1699, doi:10.1016/j.gsf.2018.06.004, Institutional Repository
de Meyer, C. M. C.; Rodríguez, J. M.; Carpio, E. A.; García, P. A.; Stengel, C.; Berg, M. (2017) Arsenic, manganese and aluminum contamination in groundwater resources of Western Amazonia (Peru), Science of the Total Environment, 607, 1437-1450, doi:10.1016/j.scitotenv.2017.07.059, Institutional Repository
Bretzler, A.; Berg, M.; Winkel, L.; Amini, M.; Rodriguez-Lado, L.; Sovann, C.; Polya, D. A.; Johnson, A. (2017) Geostatistical modelling of arsenic hazard in groundwater, In: Bhattacharya, P.; Polya, D. A.; Jovanovic, D. (Eds.), Best practice guide on the control of arsenic in drinking water, 153-160, Institutional Repository
Podgorski, J. E.; Eqani, S. A. M. A. S.; Khanam, T.; Ullah, R.; Shen, H.; Berg, M. (2017) Extensive arsenic contamination in high-pH unconfined aquifers in the Indus Valley, Science Advances, 3(8), e1700935 (10 pp.), doi:10.1126/sciadv.1700935, Institutional Repository
Bretzler, A.; Lalanne, F.; Nikiema, J.; Podgorski, J.; Pfenninger, N.; Berg, M.; Schirmer, M. (2017) Groundwater arsenic contamination in Burkina Faso, West Africa: predicting and verifying regions at risk, Science of the Total Environment, 584, 958-970, doi:10.1016/j.scitotenv.2017.01.147, Institutional Repository
Rodríguez-Lado, L.; Sun, G.; Berg, M.; Zhang, Q.; Xue, H.; Zheng, Q.; Johnson, C. A. (2013) Groundwater arsenic contamination throughout China, Science, 341(6148), 866-868, doi:10.1126/science.1237484, Institutional Repository
Winkel, L. H. E.; Trang, P. T. K.; Lan, V. M.; Stengel, C.; Amini, M.; Ha, N. T.; Viet, P. H.; Berg, M. (2011) Arsenic pollution of groundwater in Vietnam exacerbated by deep aquifer exploitation for more than a century, Proceedings of the National Academy of Sciences of the United States of America PNAS, 108(4), 1246-1251, doi:10.1073/pnas.1011915108, Institutional Repository
Amini, M.; Abbaspour, K. C.; Berg, M.; Winkel, L.; Hug, S. J.; Hoehn, E.; Yang, H.; Johnson, C. A. (2008) Statistical modeling of global geogenic arsenic contamination in groundwater, Environmental Science and Technology, 42(10), 3669-3675, doi:10.1021/es702859e, Institutional Repository
Amini, M.; Mueller, K.; Abbaspour, K. C.; Rosenberg, T.; Afyuni, M.; Møller, K. N.; Sarr, M.; Johnson, C. A. (2008) Statistical modeling of global geogenic fluoride contamination in groundwaters, Environmental Science and Technology, 42(10), 3662-3668, doi:10.1021/es071958y, Institutional Repository
Winkel, L.; Berg, M.; Amini, M.; Hug, S. J.; Johnson, C. A. (2008) Predicting groundwater arsenic contamination in Southeast Asia from surface parameters, Nature Geoscience, 1, 536-542, doi:10.1038/ngeo254, Institutional Repository