Efficient hot water distribution systems are designed to generate hot water using fewer fuel resources, and to get hot water to low-flow faucets and fixtures more quickly. These systems often feature carefully designed plumbing lines that are less redundant and/or shorter. Rather than measuring time to hot water at a fixture in gallons, efficient distribution systems can be measured in cups. EPA WaterSense Guide for Hot Water Distribution as well as several green building programs have further details. This may also be known as Structured Plumbing.