Fig. 1

a Geographical distribution of chronic kidney disease of multi-factorial origin (CKD-mfo) in Sri Lanka, illustrating the most affected areas; the North Central Province (NCP; illustrated in pink, red, and black) and the recent spread of the disease outside the NCP region (indicated in blue dots). b A map of Sri Lanka illustrating the distribution of groundwater hardness. The distribution of hard water, salinity, or ionicity does not correspond with the prevalence distribution of the CKD-mfo in Sri Lanka (lack of correlation, a, b). c A map illustrating the climatic zones of Sri Lanka: dry, intermediate, and wet zones. d A map illustrating the major rivers draining to the sea in Sri Lanka to illustrate their lack of relationship with CKD-mfo affected areas, except the River Mahaweli (indicated by blue arrows). The blue area indicates the most affected region, to which the River Mahaweli, the longest river in the country, supplies irrigated water