Summary: An introduction on A. W. Phillips ``hydraulic'' macroeconomic models is given. His (and others economists') notion that a macroeconomy may reasonably be considered to have dynamics corresponding to a first-order time lag transfer function, is justified in this paper by aggregation of individual micro agents. In connection with this economic application, we derive and discuss a theorem and some rules for general networks of time lagged blocks. Finally, Monte Carlo simulations of networks of micro agents are undertaken, supporting the validity of the first-order time lag aggregate model.