What are the smart and effective ways for cities and townships to store water during rains?

Many cities around the world face the dual problem of water scarcity and floods at different times of the year. If the excess rainwater could be collected and stored in better ways, perhaps the challenge of water scarcity could be mitigated to a significant extent. What are the various effective, innovative and sustainable avenues through which rainwater could be stored for dry days?

How will it have a positive impact?

Who will it have a positive impact on?