Water Industry News

How Flooding Contaminates The Water Supply

It’s very easy to take our water supplies for granted here in the UK. We simply turn on the taps and out it comes.


But as time goes on and the impacts of climate change are more keenly felt around the country – and around the world – it’s likely that we’ll start to see issues with the amount of water that we have at our disposal, with water shortages already being seen in some parts of the UK… and what supplies are available in the future are also going to be put at increasing risk from flooding.


Experts predict that the UK will see more frequent heavy and intense rainfall each year as a direct result of climate change, especially during the winter – which will increase the likelihood of different regions being hit with river and surface water flooding.


It’s not just how much rainfall we’ll see that drives up the risk of river and surface water flooding, however.


Ground permeability is a key factor in this, for example, as are ground saturation from previous rainfall, sun-baked ground, the presence of flood defences and so on. Drainage system capacity is also something that can exacerbate surface water flooding and such systems can quickly become overwhelmed during periods of heavy rainfall.


Flooding and drought risks in the UK are now being driven up by climate change, with research from the Met Office back in 2017 showing that global warming is increasing the risk of excessive record monthly rainfall totals for many parts of the country.


In south-east England, for example, the chances that winter rainfall will exceed current records are seven per cent during at least one month of the season. In addition, there could be a 34 per cent chance of breaking regional records somewhere each winter in other parts of both England and Wales.


In 2019, the UK Climate Change Committee warned that 1.4 million people in England now face a risk of 1:75 or greater of flooding, whether that’s coastal or surface water.


This means that there’s currently a 1.33 per cent chance of flooding in any given year, while the numbers at risk could rise to 1.7 million if global warming levels hit 2 degrees C above pre-industrial temperatures.


What does this mean for our water supplies?

Flooding has a severe effect on houses, businesses, infrastructure and farmland, with contaminants like chemicals, bacteria, fuel and so on travelling along with the water and building up in the natural environment.


The pollutants contained within floodwater represent serious and significant risks to wildlife, people and the environment, including water systems and networks, as well as private drinking water wells.


In the US, 53 million residents (or approximately 17 per cent of the population) rely on private wells, with the majority living in rural areas, according to a study carried out in part by researchers from the Environmental Protection Agency.


The Independent reports that risks to these wells increase after heavy rainfall and flooding, with contaminants like dirt, faeces and nutrients like nitrogen seeping into the wells. This threat is expected to increase over time as climate change drives stronger, wetter hurricanes and more intense rainstorms.


For example, in 2017 Hurricane Harvey caused widespread flooding in Texas, with samples of over 8,800 wells revealing average levels of E.coli almost three times higher than normal.


Floodwaters can be found in wells for days or weeks at a time and infrastructure can also be damaged by the sheer force of the water itself, which makes contamination more likely, as well.


Stormwater runoff, that which doesn’t soak into the ground, is another problem that can have an impact on water supplies and drinking water quality.


In towns, cities and other built-up areas, impermeable surfaces like pavements and driveways are more common than in rural communities, which means that larger volumes of stormwater runoff can accumulate, bringing with it contaminants such as animal waste, oil, pesticides and so on – all of which affects water quality.


How is flooding risk being managed?


Flood defences can help increase resilience against flooding, as can natural flood management, such as changing land management practices so that soil is able to absorb more water and restoring bends in rivers to slow the rate of water flow. Trees can also be planted in river catchments to help intercept rainwater.

In some parts of the country, beavers are also being reintroduced to help increase flood resilience. A five-year study led by the University of Exeter found that these keystone animals are able to alleviate flooding, boost wildlife populations and reduce pollution.


Where water quality is concerned, beavers can help drive improvements by storing nutrients, sediment and pollutants in the ponds they create.


The faster rivers flow, the more sediment they carry, bringing along fertilisers and pesticides for the ride, which can affect the water itself. When dams are built, water is slowed and the sediment then drops out of the water and accumulates on the pond bed. Beaver dams can also help reduce flooding by storing water in wetlands and ponds, slowing the flow of floodwater.


For urban communities, sustainable urban drainage systems are being introduced to reduce the risks of flooding. These systems store rainfall and surface water runoff, thus reducing how much water enters the drains and sears, helping to prevent them from being overwhelmed.

Between 2015 and 2021, risk management authorities invested £2.6 billion of government funding in flood and coastal risk management – and it’s important to note that it’s impossible to completely eliminate the risks altogether… which means it’s essential to prioritise adaptation to climate change and flooding, as well as mitigation.


The Environment Agency is now calling for a broader range of actions to make places more climate resilient, including nature-based solutions to store floodwaters or slow water flow and stopping inappropriate development in floodplains.


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