The phrases water scarcity, water stress and water shortage get used when discussing different global water issues.
In the guide below, we provide a description of what each one is, list the key differences between them, and also explain how they relate to each other.
What Does Water Stress Mean? (A Definition)
Water stress is a term used to describe the ratio of freshwater withdrawals (which essentially equals freshwater demand), to total renewable freshwater resources.
Water stress can be rated on a scale anywhere from very low to very high (or extreme)
High water stress means that withdrawals (demand) are outpacing renewal rates, and there essentially isn’t enough water resources if this trend continues
High withdrawal vs renewable rates lead to diminishing freshwater resources, and also greater competition for the remaining finite freshwater resources
Lower water stress means that total freshwater resource renewal rates are outpacing freshwater withdrawal/consumption rates i.e. supply outweighs demand
So, the point of water stress is reached when demand exceeds available resources
Some reports assign ratio %’s to different levels of water stress
Low water stress for example might be when withdrawals are less than 10% of internal fresh water resources annually.
High water stress might be when withdrawals are between 40 to 80% of internal fresh water resources annually.
Very high or extreme water stress might be anything above 80%.
Some other reports measure and express water stress with a m3 per person per year number.
Something about water stress to note is that water generation methods like desalination may increase the amount of available water a city or town has to withdraw from.
It’s also worth noting that there not only has to be enough internal freshwater resources to withdraw from, but these resources have to be available, accessible, and safe to use and consume too.
Some other descriptions of water stress from other reports are provided below …
Water stress is defined based on the ratio of freshwater withdrawals to renewable freshwater resources
If water withdrawals exceed available resources (i.e. greater than 100 percent) then a country is either extracting beyond the rate at which aquifers can be replenished, or has very high levels of desalinisation water generation (the conversion of seawater to freshwater using osmosis processes)
From wikipedia.org: ‘Much of the water stressed population [in the world] currently live in river basins where the usage of water resources greatly exceed the renewal of the water source.’
[The World Resources Institute (WRI) … defines water stress categories based on the percentage of withdrawals to renewable resources, and the categories are as follows:]
<10% = low stress
10-20% = low-to-medium stress
20-40% = medium-to-high stress
40-80% = high stress
>80% = extremely high stress
One definition of water stress from pacinst.org is: ‘… [if] the amount of renewable water in a country is below 1,700 m3 per person per year, that country is said to be experiencing water stress …’
What Does Water Scarcity Mean? (A Definition)
Water scarcity is might be considered a severe water issue.
It’s the point where there isn’t enough freshwater resources to meet the basic demand for freshwater in a city or town.
Some describe it as extreme water stress.
At the point of water scarcity, water demand (the withdrawal rate) usually exceeds the renewal rate of internal water resources, and the volume of available freshwater resources might have declined to a low level.
Water scarcity categories might include regular water scarcity, but also absolute or extreme water scarcity.
There might be two main types of water scarcity – physical water scarcity (which involves physical access and availability problems), and economic water scarcity (which involves a lack of financial investment and resources, or mismanagement of water resources by the government or other management groups)
Perth in Western Australia is an example of a city that experienced water scarcity, but has since addressed it with technology such as desalination and ground water replenishment (amongst other measures)
One definition of water scarcity from pacinst.org is: ‘… [if] the amount of renewable water in a country is … below 1,000 m3 it is said to be experiencing water scarcity; and below 500 m3, absolute water scarcity’
There’s several ways to measure or assess water scarcity, which globalwaterforum.org outlines in their guide.
A paraphrased list of these ways to measure or assess water scarcity might be:
– Measure the amount of renewable freshwater available per capita, per year
– Measure total water demand compared to total water available
– Measure internal fresh water available, alongside fresh water consumption, and take into account each region’s existing water infrastructure, whilst also consider that region’s ability to adapt in the future by building additional infrastructure or using technology to address any water scarcity related problems [this approach can help delineate between economically, or physically water scarce countries – both are which are different. Income and wealth of a region play a role in economic scarcity]
– Measure the level of access to water, water quantity, water quality, water variability, water consumption, competence of water management and also any external or environmental aspects that may impact upon the water supply (like rain, climate, droughts, and so on).
Water scarcity might be more accurate on a city or town level, but can also be calculated on a State/Province, or national level.
What Is A Water Shortage? (A Definition)
The term ‘water shortage’ is often used to describe the same conditions as water scarcity, and they are sometimes grouped as the same issue or event.
‘Water shortage’ is a phrase sometimes used to describe a specific type of extreme water scarcity event where clean fresh water resources are getting to low enough levels where extreme water restrictions (say, level 7 or 8 water restrictions – sometimes called ‘Day Zero’) have to be enforced, and municipal tap water may have to be temporarily turned off.
Factors That Can Impact Water Stress, Water Scarcity & Water Shortages Stressed
Water Stress vs Water Scarcity vs Water Shortage: Similarities
Water stress, scarcity and shortage all mainly refer to water quantity related issues.
Specifically, they may mainly refer to a lack of water to meet the demands of a population with a geographic area (although, a lack of water access can lead to a lack of water quantity too).
Water Stress vs Water Scarcity vs Water Shortage: Differences
The main differences between water stress and water scarcity might be:
– Water stress
Is a sliding scale – it ranges from very low water stress, up to extreme water stress
Water stress is a broader water principles than water scarcity or water shortages
Lower water stress and moderate water stress may also be much less severe of issues than water scarcity or water shortages
[Water stress is more inclusive and broader as a concept compared to water scarcity because it] considers several physical aspects related to water resources, including water scarcity, but also water quality, environmental flows, and the accessibility of water (pacinst.org)
Water stress does not insinuate that a country has water shortages, but does give an indication of how close it maybe be to exceeding a water basin’s renewable resources (ourworldindata.org)
– Water scarcity
Is more specific and and more narrow of an issue than water stress, as well as being more severe
It exclusively refers to the point at which a population may be experiencing very high or extreme water stress, and exclusively refers to there not being enough freshwater resources for basic water needs in a city or town
– Water shortage
A very specific event – is essentially an emergency event in some cities or towns, similar to what Cape Town experienced.
Water withdrawals may have to temporarily shut off until water resources can be replenished to a certain level.
Potable vs Non Potable Water Supplies
It should be noted that there is a difference between potable fresh water supplies for drinking, and non potable fresh water supplies.
Cities and countries can have secure drinking water resources, but non potable water supplies may be depleting, and experiencing water stress, scarcity or shortages.
So, this is something that needs to be clarified when discussing a city’s water supplies and resources.
1. Various ‘Better Meets Reality’ guides
2. Downloads/642-progress-on-level-of-water-stress-2018.pdf, ‘Progress On Level Of Water Stress’ (from unwater.org)
5. Hannah Ritchie and Max Roser (2018) – “Water Access, Resources & Sanitation”. Published online at OurWorldInData.org. Retrieved from: ‘https://ourworldindata.org/water-access-resources-sanitation’ [Online Resource]
7. 9. https://en.wikipedia.org/wiki/Water_scarcity