Urban infrastructure investments require decision making under uncertainty given their long lifetimes and unpredictable future changes. Traditional planning that relies on predictions of a single future can lead to overconfidence and poor decisions. A better approach, called "decision making under uncertainty", develops strategies that are robust to different potential futures through identifying vulnerabilities and no-regret investments. This approach was applied for urban water supply in Lima, Peru by phasing investments based on observed changes in climate and demand over time. Stakeholder involvement is also important for balancing competing priorities under uncertain conditions.