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 focus on geogenic contaminants such as arsenic, fluoride, iron, manganese and salinity.  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 may be a result of geochemical characteristics of the aquifer material, e.g. high concentrations of the contaminant in the rock matrix that dissolve during water-rock interaction or environmental conditions such as an arid climate or reducing aquifers that favor the dissolution of the contaminant.

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, a disease associated with elevated fluoride concentrations in drinking water, is a serious health concern in many 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 and can then limit 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

Where does fluoride groundwater contamination occur?

What are the effects of fluoride on human health?

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 Bangladesh).

High arsenic concentrations in groundwater have been found to be responsible for chronic health problems that fall under the term arsenicosis and 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 only mitigation approach.

More information

Where does arsenic groundwater contamination occur?

What are the effects of arsenic on human health?

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).

GAP Team

Dr. Michael Berg Head of Department Tel. +41 58 765 5078 Send Mail

Previous contributors

  • Dr. Annette Johnson, Eawag, project Initiator
  • Dr. Chris Zurbrügg, Eawag directorate
  • Dr. Anja Bretzler
  • Dr. Dahyann Araya
  • Jay Matta, SDC / UNHCR
  • Fabian Suter, Eawag
  • Yuya Ling
  • Dr. Manouchehr Amini
  • Dr. Tobias Siegfried, Hydrosolutions
  • Jakob Steiner


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


Araya, D.; Podgorski, J.; Berg, M. (2023) Groundwater salinity in the Horn of Africa: spatial prediction modeling and estimated people at risk, Environment International, 176, 107925 (12 pp.), doi:10.1016/j.envint.2023.107925, Institutional Repository
de Meyer, C. M. C.; Wahnfried, I.; Rodriguez Rodriguez, J. M.; Kipfer, R.; García Avelino, P. A.; Carpio Deza, E. A.; Berg, M. (2023) Hotspots of geogenic arsenic and manganese contamination in groundwater of the floodplains in lowland Amazonia (South America), Science of the Total Environment, 860, 160407 (14 pp.), doi:10.1016/j.scitotenv.2022.160407, Institutional Repository
Ling, Y.; Podgorski, J.; Sadiq, M.; Rasheed, H.; Eqani, S. A. M. A. S.; Berg, M. (2022) Monitoring and prediction of high fluoride concentrations in groundwater in Pakistan, Science of the Total Environment, 839, 156058 (9 pp.), doi:10.1016/j.scitotenv.2022.156058, Institutional Repository
Podgorski, J.; Berg, M. (2022) Global analysis and prediction of fluoride in groundwater, Nature Communications, 13(1), 4232 (9 pp.), doi:10.1038/s41467-022-31940-x, Institutional Repository
Araya, D.; Podgorski, J.; Berg, M. (2022) How widespread is fluoride contamination of Ghana's groundwater?, Water Science Policy, (4 pp.), doi:10.53014/OGJS9699, Institutional Repository
Araya, D.; Podgorski, J.; Kumi, M.; Mainoo, P. A.; Berg, M. (2022) Fluoride contamination of groundwater resources in Ghana: country-wide hazard modeling and estimated population at risk, Water Research, 212, 118083 (10 pp.), doi:10.1016/j.watres.2022.118083, Institutional Repository
Podgorski, J.; Araya, D.; Berg, M. (2022) Geogenic manganese and iron in groundwater of Southeast Asia and Bangladesh - machine learning spatial prediction modeling and comparison with arsenic, Science of the Total Environment, 833, 155131 (11 pp.), doi:10.1016/j.scitotenv.2022.155131, Institutional Repository
Alam, M. F.; Villholth, K. G.; Podgorski, J. (2021) Human arsenic exposure risk via crop consumption and global trade from groundwater-irrigated areas, Environmental Research Letters, 16(12), 124013 (18 pp.), doi:10.1088/1748-9326/ac34bb, Institutional Repository
Wu, R.; Podgorski, J.; Berg, M.; Polya, D. A. (2021) Geostatistical model of the spatial distribution of arsenic in groundwaters in Gujarat State, India, Environmental Geochemistry and Health, 43, 2649-2664, doi:10.1007/s10653-020-00655-7, Institutional Repository
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