X Close

UCL Institute for Environmental Design and Engineering


Blogs from UCL IEDE Staff and Students


Water, water, everywhere…

By ucftjgt, on 13 January 2016

floodingWatching politicians wearing rubber boots wading through floodwaters is quickly becoming become an annual winter and spring tradition in the UK[1]. This year, a number of voices have attributed blame for the floods on cutbacks in flood defence spending, land use management, building construction in flood-vulnerable locations, and climate change. In reality, the flooding is likely to be a combination of all these factors. What we can say with confidence, though, is that we should expect the type of rainfall events that caused the floods to become more common in the future due to climate change – indeed, research indicates that climate change made this year’s floods across the UK 40% more likely[2]. As the risk of floods becomes greater, we need to learn how to be more resilient against floods, which requires increasing our understanding of their impact on population health and buildings.

How do floods affect population health?

The health risks from flooding include the obvious direct consequences, such as drowning or electrocution, as well as the less-obvious indirect consequences such as exposure to contaminated houses, health problems exasperated by stress, and mental health issues. In the UK, deaths due to floodwater are relatively rare, and so evaluating the public health impacts – for example increases in the rate of deaths or illnesses – largely focuses on indirect heath consequences. These are tricky to estimate since the flooded population tends to be temporarily displaced, making the analysis of health data difficult. One of the earliest studies of health consequences following flooding indicated a massive 50% increase in the population death rate following a flood in Bristol[3]. More recent studies have shown a lower mortality risk following floods, likely due to this displacement of the resident population[4].

What is clear is that flooding can be a traumatic experience for victims, with a number of mental health consequences that can arise particularly in the more vulnerable segments of the population[5], and that living in a damp house may lead to a number of physical health issues[6].

Impacts on Housing

Water pressures from high or fast-moving floodwaters, or soil erosion may lead to structural damage. However, the most typical damage occurs when floodwater comes into contact with building materials and water is drawn into the material through a combination of capillary forces and the pressure from the water.  Damp air may move around a building, such that even surfaces that were not directly flooded may become damp. Sediment from floodwater may deposit on the surfaces and move into the pores of the building materials.

Damp surfaces in flooded houses may enable the growth of mould and bacteria, and the survival of different harmful bacteria that may be present in floodwater; the presence of sediments may encourage growth. Mould and bacteria may release spores, toxins, cell fragments, and other organic compounds into the indoor air which may cause a number of health problems in building occupants, particularly children[7]. It is therefore very important that houses be dried well before they are inhabited again. And, since these contaminants can enter the indoor air from wall cavities and subfloors, this means completely dry, not just surface-dry.


It can take a very long time to dry out homes following floods – following the 2007 floods in Hull, there were reports of 10% of households still living in temporary housing two years after the flood[8]. This is due to the limited resources of restoration companies, as well as the unfortunate prioritisation of commercial rather that residential properties in order to help with economic recovery.

Like with flooding, the drying behaviour of housing can vary depending on how the buildings are constructed as well as the ability to ventilate the property. Different materials respond in different ways to water; some, such as traditional brick may absorb water but dry out relatively easily, while others such as aerated concrete may be difficult to dry. Sediments or salts in the flooding water may make drying more difficult. Some materials, such as glass fibre or vermiculite insulation may actually retain water even when the surfaces of the walls may appear dry. It is therefore important to check moisture levels inside the wall.

Buildings will not dry unless damp air is removed from indoors, which means that buildings that can be well ventilated will dry faster. Heat will help accelerate drying, but only if performed alongside ventilation – heat by itself runs the risk of introducing hot, humid conditions which may encourage microbial growth.

If you are unfortunate enough to have your house flooded and don’t want to wait for professional help, remove any sediment from inside the house and then try to both ventilate and heat the house as much as possible. Always wear gloves when touching surfaces and a respirator mask if there are signs of mould growth. And, first and foremost, be safe – it is unlikely that there is anything inside your home worth risking your health for.

[1] http://www.buzzfeed.com/jimwaterson/pictures-of-politicians-in-wellies-and-staring-at-floods#.glll91E6lR

[2] (http://www.theguardian.com/environment/2015/dec/11/storm-desmond-rainfall-flooding-partly-due-to-climate-change-scientists-conclude).  Recent cuts to flood defence spending are likely to have exasperated the situation

[3] Bennet G. Bristol floods 1968: controlled survey of effects on health of local community disaster. British Medical Journal. 1970;3: 454–458.

[4] Milojevic A, Armstrong B, Kovats S, Butler B, Hayes E, Leonardi G, et al. Long-term effects of flooding on mortality in England and Wales, 1994-2005: controlled interrupted time-series analysis. Environmental health 2011;10(1):11.

[5] Norris FH. Range, Magnitude, and Duration of the Effects of Disasters on Mental Health: Review Update 2005. Dartmouth; 2005.

[6] WHO. World Health Organisation Guidelines for Indoor Air Quality: Dampness and Mould. Copenhagen; 2009.

[7] WHO. World Health Organisation Guidelines for Indoor Air Quality: Dampness and Mould. Copenhagen; 2009.

[8] Hull City Council. Two years on – 2009. Technical report, Hull City Council, 2009.

Leave a Reply