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I live in the exact area you visited, glad you liked it! indeed all cemeteries have a water point to fill containers in order to water plants and flowers.
At some point last summer in places where water was a bit of a concern they closed some water taps in cemeteries to save water, but most of the time they are open.Also for you that travel through France, in almost all cities (even small ones) you can find football fields, and around them near changing rooms there are water points as well in the exterior. Those ones can be closed (cemeteries are more reliable sources), but can be life-savers as well sometimes.
There is always drinkable water in cemeteries too, which is useful to know.