Rainwater is water accumulated from precipitation.

Rainwater catchment systems or cisterns catch and store rainwater for uses such as irrigation, plumping, or cooling towers, thereby reducing stormwater runoff.

Rapidly renewable materials and products are materials considered to be agricultural products, both fiber and animal, that take 10 years or less to grow or raise, and are harvested in an ongoing and sustainable fashion. Examples include bamboo, cork, wool, cotton, agrifiber, linoleum, wheatboard, and strawboard.

Reclaimed water is wastewater that has been treated and purified for reuse.

Recommissioning applies to buildings that were previously commissioned as part of new construction or buildings covered by existing building commissioning.

Recyclable materials can be easily recycled and reused in the future.

Recycled materials are made of previously used resources or products (as opposed to virgin materials).

Renewable energy, or green power, comes from natural resources that can be naturally (and relatively quickly) replenished, such as sunlight, wind, rain, tides, biomass, biofuels, geothermal, and ground source heat.

Renewable Energy Credits/Certificates, (RECs), are tradable commodities representing renewable energy. RECs are purchased in addition to grid electricity to offset non-renewable energy used with renewable sources. RECs fund renewable energy sources and contribute renewable energy to the national grid, thereby reducing fossil fuel based energy production. Rocs purchased to achieve LEED points must be certified Green-e (a third-party certifier) or meet equivalent standards. Green power is another term often used for Rocs.

Runoff is a term used to describe when soil is infiltrated to full capacity with excess water, from rain, snowmelt, or other sources. This is a major component of the water cycle. When runoff flows along the ground, it can pick up soil contaminants such as petroleum, pesticides (in particular herbicides and insecticides), or fertilizers that pollute water sources.