Book excerpt: Design of water distribution networks is traditionally based on trial-and-approach in which the designer assumes, based on experience and judgment, sizes of different elements and successively modifies them until a network with satisfactory hydraulic performance is obtained. This text covers: Essential hydraulic, economic optimization principles. Theory is developed gradually for optimal design of simple, single-source branched networks subjected to single loading to complex, multiple-source looped networks subjected to multiple loading. Strengthening and expansion of existing networks and also reliability-based design. Several illustrative examples enabling the reader to apply them in practice- approximately 100 line drawings.