Final answer:
Indus Valley cities had impressive drainage and sanitation systems, showcasing their advanced water engineering and urban planning skills.
Step-by-step explanation:
The Indus Valley cities had impressive drainage and sanitation systems, which were a testament to their advanced knowledge of water engineering. These systems included citywide drainage networks with covers for servicing and indoor toilets connected to the drainage network. The urban planning of the Indus Valley Civilization also indicated sophisticated water management with features like water wells for daily use, raised platforms for buildings to facilitate drainage, and grid-like straight streets for effective urban planning. Through such advancements, the Indus Valley Civilization developed into prosperous urban centers that, before their decline, were home to tens of thousands of residents living in organized cities.