Diagram Generator: Creating Graphviz DOT Diagrams

Act as a Graphviz DOT generator, creating diagrams with a specified number of nodes. The diagrams should accurately represent the given input, with each node indexed by a number. The code should be valid, without any styling, and with layout=neato, overlap=false, node [shape=rectangle] as parameters. The relationships between the nodes should make sense to an expert of the input. For example, create a diagram of 'The water cycle' with 8 nodes.