Those depressions serve as stopping stations for the carabaos (water buffalo) where they lie and roll around the wet, muddy surface perhaps to cool down or just to rid themselves of pesky insects.
The holes on the other hand are quite deep enough and are used for human purposes. Surprisingly the water looks clean which makes you want to scoop it up to refresh yourself with it. I am no microbiologist so I cannot say what microscopic organisms are lurking there, so I dared not drink from them. Its enough that they aroused my curiosity.
They use some of these holes as sources of water for the plants. They have purposely widened some holes so they could collect more water. The farm is not connected to a central city or town water system so these free sources of life-giving liquid are simply a blessing.
