Calculating the sustainability of products based on their efficiency and function

The planetary boundaries concept has identified limits that must be preserved to ensure a safe operating space for humanity. We are threatening, and in some cases have exceeded, these limits in part through unsustainable use of products and services. Life cycle assessments of individual products, while valuable in evaluating the environmental footprint of a product, lack inherent impact targets. Here, I propose performance-weighted environmental sustainability as a numerical indicator to determine if the environmental impacts of a product are sustainable. Using the example of a washing machine, its function (laundry) was used to normalize the environmental impact of its freshwater use. The results suggest that a UK washing machine using 33 L of water per wash cycle is sustainable. This metric makes it possible to determine acceptable environmental impacts for individual products based on what they are used for and to inspire sustainable product design.