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Hmmm, tricky one! It depends how you define "ODF". Open Defecation often wasn't the biggest issue: it was people using poor toilets, foe example flush toilets that would go directly in the river. A lot of the history focuses on improved legislation and "landmark" improvements like the extension of sewers in large cities like London or Paris. In rural areas you would find an outhouse / pit toilet quite readily. The statistics I have seen tend to be for particular cities or even settlements. Useful resources: https://wedc.lboro.ac.uk/resources/well/WELL_BN10_Learning_from_the_past.pdf quotes that "in the 1930s, there were still appalling conditions in industrial towns" in the UK. Or more recently, in France there were still many slums in the 1950s that had very poor sanitation. This resource https://hdr.undp.org/sites/default/files/bryer_helen.pdf also points some useful data. What can be generally remembered is that, while big changes were triggered in the second half of the 19th century, and while many large improvements happened in big cities then, progress in smaller industrial towns and cities and in rural areas took more time, well into the 20th century...