Explanation
Non-potable water is water that is not suitable for human consumption, but can be used for other purposes that do not require potable quality water. Non-potable water sources include rainwater, reclaimed/recycled water and greywater. Greywater is wastewater from sinks, showers, bathtubs, washing machines and dishwashers that can be reused for applications such as toilet flushing, irrigation and cooling tower make-up water12. Using non-potable water can reduce the demand for potable water and contribute to LEED water efficiency credits34.
References :=
SRI Calculator | LEEDuser
What Is Solar Reflectance Index (SRI) of Materials?
Water Efficiency and LEED Certification | Contractor
Water Balance Analysis - ASHRAE
What is LEED? | Net Zero Water Inc. - Net Zero Water

Explanation
Water Efficiency is the only credit category that does not have a prerequisite in LEED v4 for Building Design and Construction. Prerequisites are the minimum requirements that all projects must meet to be eligible for LEED certification. They are mandatory and non-weighted, meaning they do not contribute to the project's score. The other credit categories have at least one prerequisite each, as shown in the table below:

References: LEED v4 Reference Guide for Building Design and Construction, p. 17 1; [LEED v4 BD+C Scorecard]

LEED rating systems are designed with 100 base points for core credits, six bonus points for Innovation, and four bonus points for Regional Priority credits. This structure allows projects to achieve a total of 110 points, reflecting LEED's flexibility and comprehensive approach.