What are the four water sources, referred to as "taps," that sedlak believes will solve our urban water crisis?

Answer:

Local water source, recycled water from sewage treatment plants, water conservation from outdoor water use and generating water from desalinated seawater are the four water sources referred to as "taps," that Sedlak believes will solve our urban water crisis.

Explanation:

David Sedlak is an civil and environmental engineer in USA, who has shared four practical solutions to existing water crisis. His objective is to create a model system where water crises can be minimised by shifting the interest from the current source water supply. He suggested four ways or taps from where water can be obtained in order to prevent occurrence of catastrophic drought due to usage of water from a single source.