Groundwater - a non-renewable resource?

The theme of World Water Day 2022 is Groundwater: Making the invisible visible. Our Principal Hydrogeologist Dr Catherine Isherwood took the opportunity to explore the idea of groundwater being considered a ‘non-renewable’ resource. She discusses the value of groundwater and how work by her team aims to conserve it.

In many parts of the world, groundwater forms the principal source of water for drinking, agriculture and industry.

Groundwater is the term used to describe water that is held within the ground. The water can be held within soils and sediments, such as sand or gravel deposits, or within rock. There aren’t usually rivers or lakes underground, like the ones we have at the surface.

Groundwater is useful because it can often be accessed in areas where surface water is scarce, absent or seasonal. It is also not susceptible to the same levels of biological contamination as surface water and is less likely to contain significant levels of suspended sediment, although both can occur under some circumstances.

Groundwater won’t run out, but fresh groundwater may become so scarce in parts of the world that they no longer have a source of fresh water for drinking, agriculture and industry.

The demands on water supplies from increasing populations, increased development and climate change mean that in many areas more groundwater is being abstracted than replaced. This leads to an overall decrease in groundwater levels. This is not occurring at the same rate in all areas – some parts of the world have higher demands on groundwater than others, and some areas also have larger groundwater resources available to use. Areas of high demand and low availability experience groundwater scarcity.

A lot of groundwater is not suitable for our use as it contains high levels of mineral salts or other dissolved material that make it unpotable. 

Groundwater in coastal regions can be salty, like the sea. Groundwater that has been in the ground for thousands of years or longer usually has very high levels of dissolved minerals which make it unsuitable for drinking, agriculture or industry. Sometimes the dissolved minerals are dangerous – for example, arsenic is toxic, and high doses of fluoride can affect teeth, bones and major joints in a condition known as skeletal fluorosis, which can cause serious disability.

Highly mineralised groundwater is also not usually suitable for agriculture, as it can kill or damage crops and can negatively affect soil fertility over time. It may also cause problems in industrial situations through damage to machinery and pipework.

We need to improve our water efficiency, so that we all use less water for everyday purposes. 

Water use per person in western countries is very high – for example, in the UK the average water use per person is about 142 litres per day; in the USA, this is approximately 310 litres per person per day. Using more water-efficient appliances, including dish washers and washing machines, and dual-flush toilets can help to reduce water usage, as can taking shorter showers or showering every two days rather than every day. Turning the tap off when cleaning your teeth can also help!

Thinking about produce that we buy can also influence our individual ‘water footprint’. For example:

• Cotton requires around 10,000-20,000 litres of water to cultivate one kilogram of raw cotton.
• Fresh fruit and vegetables grown in dry areas, like southern Spain, parts of Africa and India can exacerbate water abstraction in these areas through the need for irrigation, leading to over-abstraction of groundwater.
• Almonds are a very water-hungry crop, and in California (which produces 80% of the world’s almonds) water use is estimated at 2000 US gallons (approximately 7,570 litres) per pound (450 g) of almonds. California has experienced severe drought conditions repeatedly since 2000, with the longest period lasting from December 2011 to March 2019, 376 weeks. California is currently in a drought condition lasting from early 2020.

Changes in weather patterns have had an impact on groundwater recharge. 

Higher intensity storms, where a very high level of rain falls in a short period of time, are more likely to cause flooding and are less able to contribute to groundwater recharge as the water runs off the ground too fast. For groundwater recharge to take place, we need to slow the water down so that it has chance to soak into the soil and through into the rock below.

Our habit of creating hard surfaces, like roofs, tarmac roads and surfaced parking areas, also mean that rainfall and surface water can’t get into the ground. This water goes into the drainage network and can also lead to increased flood risk downstream. If we had more permeable surfaces, such as vegetated areas, green roofs, permeable paving and temporary storage ponds where the water can collect and soak into the ground, this would help both to mitigate flooding and also to improve groundwater recharge. In the UK, this is particularly important in the south and east of England, where we have the highest density of built-up space and the highest dependence on groundwater for water supplies.

We need to improve our water management infrastructure, to include measures like collecting rainwater for use in non-potable situations such as for toilet flushing or irrigation. 

Land use change, that can help to slow runoff water down and hold it in temporary storage areas, can help to improve recharge of the groundwater resources. Using irrigation and industrial water more efficiently can help to reduce water wastage.

WRc and RSK provide advice to clients over their water use, providing business-specific water strategies to help reduce water use.

We are involved in modelling water use and water abstractions, to ensure that only the volume of water required is abstracted from surface or groundwater sources. This includes modelling dewatering associated with excavations or cuttings, to permit construction works in a dry environment or to inform long-term drainage design, as well as modelling water abstraction for water usage requirements.

Our teams undertake drainage impact assessments considering water management for developments, which includes design of sustainable drainage systems. These can be valuable in managing water flow as well as in water treatment, and help to contribute to groundwater recharge from detention and settlement ponds, swales and filter drains as well as helping to mitigate downstream flood risk.

We undertake assessments of sensitive habitats associated with groundwater, to determine if proposed construction works may affect their water supply. As part of this, we advise clients on development design so that any potential effects can be avoided or mitigated through good design principles.