Retrofitting water into places that are already built is a different problem to designing for a greenfield site. The catchment is fixed, the space is contested, and the works have to happen around people who are still using the street.
Water in constrained space
Passive irrigation and street tree watering designed into new road alignments, sized against a water balance for the specific species and the catchment actually available to each tree.
Working around existing infrastructure
Diverting flows to somewhere maintainable when the obvious location has no truck access. Incorporating existing assets rather than replacing them. Keeping pedestrian and cycle movement safe while the works go in.
Greening as part of the outcome
Urban renewal projects usually want canopy as much as they want drainage. Designing the two together means the trees get the water they need without a separate irrigation system to maintain.