"Waste not, want not" ... "A stitch in time saves nine"

This principle brings together traditional values of frugality and care for material goods, the mainstream concern about pollution, and the more radical perspective that sees wastes as resources and opportunities.

The industrial processes that support modern life can be characterised by an input-output model, in which the inputs are natural materials and energy while the outputs are useful things and services. However, when we step back from this process and take a long-term view, we can see all these useful things end up as wastes (mostly in rubbish tips) and that even the most ethereal of services required the degradation of energy and resources to wastes. This model might be better characterised as "consume–excrete”. The view of people as simply consumers and excreters might be biological, but it is not ecological.

Bill Mollison defines a pollutant as "an output of any system component that is not being used productively by any other component of the system”. This definition encourages us to look for ways to minimise pollution and waste through designing systems to make use of all outputs. In response to a question about plagues of snails in gardens dominated by perennials, Mollison was in the habit of replying that there was not an excess of snails but a deficiency of ducks.

The earthworm is a suitable icon for this principle because it lives by consuming plant litter (wastes), which it converts into humus that improves the soil environment for itself, for soil micro-organisms and for the plants. Thus the earthworm, like all living things, is a part of a web where the outputs of one are the inputs for another.

The proverb "waste not, want not"reminds us that it is easy to be wasteful when there is an abundance but that this waste can be the cause of later hardship. "A stitch in time saves nine"reminds us of the value of timely maintenance in preventing waste and work involved in major repair and restoration efforts.