What is a water footprint?

In this step we’ll introduce you to the concept of the water footprint, and show why the concept is relevant to consumers, industry, and government.

Where possible we use examples of water use to illustrate the concept.

The purpose here isn’t to delve deeply into the methods used in estimating water footprints, but rather that you gain some understanding of the wider implications of household and industry consumption on global water use.

After completing this activity you should be able to think more critically about:

• how much water we actually use in the process of consumption
• what we mean by direct and indirect water use
• what we mean by water embedded in trade
• how one might reduce one’s water footprint

The actual definition of a water footprint varies according to what we are attempting to measure, but a water footprint might be understood as:

“直接和间接使用的水量（在短期内无法重复使用）来支持人类的消费活动。”

Importantly the footprint concept allows us to estimate water use at different geographical scales and with these estimates of use to different groups. Then a water (and carbon) footprint might be estimated for a person, household, town, region, nation or globally.

When considering water footprints for regions and nations we also need to think in terms of virtual water i.e. the amount of water that is embodied in trade flows.

For example, when a nation imports agricultural products there was water employed in their growth and production, and that water is embodied in that trade flow, much the same as carbon and greenhouse gas emissions are also embodied in a nation’s trade.

What do we mean by water used?

Within this broad definition there’s also a need to think about different types of water. For example, there will be some freshwater resources which are ‘used’ but then return to the ‘system’ being available for almost immediate reuse. Then a comprehensive analysis of water footprints might differentiate:

• Green water footprint:volumes of water stored in soil from rainfall that is for example evaporated to produce a product, or used by plants. This is important when considering water used in agriculture and forestry.

• Blue water footprintthe volume of freshwater consumed from global water bodies such as rivers, lakes etc. Here water might be taken from a lake or river and used in production processes or simply used and returned into another water body. So, for example, in the UK our direct household water consumption will have a blue water footprint, as will some UK industry use.

• Grey water footprint– this is the volume of water needed to dilute pollutants for discharge to agreed regulatory standards.

Diagram of the UK Water Footprint

水足迹的概念是关于测量和方法的有争议的争论。

In the next steps we will consider some simple scenarios to illustrate different thinking around how consumption and production decisions of industries and households impact water resources.

Over to you

• How would you estimate your water footprint?
• High or low? and why?

Let us know in the comments.