A fresh approach to country ponds--by way of city puddles--adds interest to this latest lesson in ecology by the pair responsible for once There Was A Tree (1968). We see puddles forming, evaporating, emptying into sewers, sometimes depositing enough soil at their entrance for plants to grow; ""You can follow the water trail"" from a flushing truck, the authors remind us. Then to the country where ""the land is unpaved and uneven--the way the city used to be."" Here is the familiar community of animals in the water, on the water and around its edges (the latter represented by tracks--""clues to night visitors and night happenings""). The incitement to look closely, and the close-up photos--along with the sudden drama of a heron seen waiting, a snail seen crawling, the heron snapping up the snail--make this immediate and involving. If it is not as didactically ordered as others (modes of interdependence are suggested but not always spelled out), it is nevertheless--for the younger city child especially--an inviting view of water as a life-supporting element.