Why not just build the traditional water systems instead of decentralized systems?

The cost of extending or installing traditional or centralized water and wastewater infrastructure is not feasible for many municipalities. Small and rural communities do not have the tax base or the growth rate of an urban area to support this. These municipal systems are designed for over-capacity to accommodate growing populations, where decentralized systems are modular and can be expanded as needed and are likely better suited for the slower rate of growth in rural communities.