You can earn this credit simply by eliminating turf grass, planting native and adaptive species, and not installing an irrigation system. If those measures go too far for your project, you can still achieve the credit as long as you have some flexibility with plant species selection, and irrigation system design and controls. You may need a landscape designer to identify local or adaptive plant species that require little irrigation, to design water-efficient irrigation systems, to address the potential use of non-potable water, and to reduce irrigation needs through zoning, grouping, and grading of the landscape.
If you install irrigation
If you do install irrigation, you must perform calculations to show the savings of the project design versus a baseline. Usually done by the landscape architect or architect, these calculations determine the percent reduction of total water applied and total potable water applied. Projects with landscaping on less than 5% of their site area cannot earn points here, so consider planters or small gardens to meet that threshold.