This Technical Practice Update (TPU) introduces municipal wastewater system owners and operators to a risk-based approach for determining the capacity of their collection and treatment systems and compares the risk management approach to capacity and sizing decisions with traditional approaches. This TPU is not meant to provide detailed protocols for a risk-based approach, rather, how the decision framework can be applied to wet weather alternatives analysis and level of service determinations. This TPU includes the following sections: Introduction, Background, Sanitary Sewer Overflow Risk Background, U.S. Environmental Protection Agency's Proposed Sanitary Sewer Overflow Rule, Historical and Current Capacity Sizing Approaches, Traditional Approaches, Current Water Environment Federation Approach, Step 1 - Define Value and Risk, Step 2 - Identify Possible Risks, Step 3 - Evaluate Risks, Step 4 - Develop Risk-Reduction Strategies, Step 5 - Prioritize Risks Reduction, Step 6 - Risk Management Plan, Conclusions, Recommendations, and References. Published by WEF. 2007. Electronic download. 39 pages.