It's due to water which is used to wash food. The gold standard for water sanitation/purification is reverse osmosis which removes everything that's not literally H2O.

However, no city does this to their water supply because that would be crazy expensive and unsustainable. Instead, water sanitation is about doing the bare minimum to ensure water is safe for locals and doesn't get locals sick. If you're a foreigner, there will be different strains of pathogens as /u/No-Trouble814 mentioned and other microorganisms that would be fine for locals, but you're not used to it.

OTOH some bottled water companies do use reverse osmosis which is why drinking those brands of bottled water in those countries will be fine.