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Water safety (waterborne diseases and immersion)


(Published January 2022, replacing June 2005)


Before doing any water activity it’s important to understand the key hazards and risks associated with being in the water. This guidance provides an overview and signposting to more information on issues relating to immersion (being in the water) and some of the diseases and illnesses which may be contracted through exposure to open water environments.

Cold water can be extremely dangerous and can have extremely harmful effects on the human body. There are two main kinds of immersion – short term and long term.

The main problems that are associated with this form of immersion involve the circulation of the blood and the breathing system. When a person drops into cold water, the blood vessels nearest to the skin constrict and the blood pressure in the body core rises rapidly. Together with an increase in heart-rate due to the alarm felt by the person, this can lead to heart failure in some people. On rare occasions this can happen to apparently healthy young people.

The second type of response is where immersion is accompanied by big involuntary gasps. During this period a person can be inhaling and exhaling up to five times the normal volume of air. This greatly increases the possibility of inhaling water and drowning. A complication is that, during this process, the level of Carbon Dioxide in the blood is reduced and fainting can occur. An unconscious person is more likely to inhale water and drown. The changes in blood chemistry involved increase the possibility of muscle cramps, and decrease the ability to survive.

In order to minimise these effects, enter the water as gradually as possible, and consciously attempt to control the breathing rate. The more clothing and insulation worn, the greater chance of avoiding these effects and surviving, this must be balanced with the weight these items become when they absorb water, using specialist equipment such as wetsuits and lightweight waterproof fabrics is preferable.

In general those people accidentally immersed in cold water, who have some sort of flotation device (life jacket or buoyancy aid), do not die as a result of the short term problems discussed above. The danger in the long term is the progressive loss of body-heat leading to hypothermia,
unconsciousness, inhalation of water, and death (either from drowning or loss of heat).

In the average person it takes from 15 to 20 minutes for the core of the body to begin to cool. When the core temperature has dropped from the normal 37C to about 34C, a maximum rate of shivering by the body is reached. The heat generated by this shivering is, however, only sufficient to match heat loss in cool air and so the cooling continues. Below 35C, experimental patients tend to lose the ability to maintain a logical sequence of ideas. This could be the reason for the strange behaviour often noticed in hypothermia victims.

The wearing of protective clothing can delay the cooling process and the onset of hypothermia by considerable amounts, depending on the degree of specialisation of the clothing. For example, an unprotected person in 10C water will see their core temperature drop from a normal 37c to a dangerous 33c in about 45 minutes.

If someone ends up in the water and unable to reach help they should minimise their movement to conserve heat and this can be optimised by adopting the Heat Exposure Lessening Position (HELP). By adopting this crouching position, the areas of greatest heat loss (the head, neck, sides and groin) can be protected.

If a group of people find themselves in cold water together, they can adopt the HUDDLE position, where the group gathers together and link up to reduce their surface area exposed to the water.

Treading water uses up body energy which means that heat is being lost more rapidly than if simply floating in your lifejacket or buoyancy aid. Any person regularly undertaking water activities in water which has a temperature of less than 15C, should practice HELP and HUDDLE techniques regularly, so that if there is an emergency they come automatically to mind.

Hypothermia happens when the body gets dangerously cold (the body temperature drops below 35C). It can creep up on someone without them realising as it can occur from longer term exposure as well as immediate exposure such as falling into cold water. Hypothermia is a real risk for those taking part in water activities but can be prevented with preparation, equipment and other controls.

You can view the symptoms and treatment for hypothermia on the NHS website.

Water, including flowing river water, may be contaminated for example from sewage discharges and overflows, land run-off or discharge from water vessels. The level of contamination can change significantly and quickly, for example after heavy rain. This can create a potential risk to anyone using the water, therefore water quality should be considered prior to any water activity.  Factors to consider include the locations of sewage discharges and overflows, potential areas of stagnant water, adjacent land use and recent rainfall. No water based activity should proceed if there are any concerns around water contamination in the planned location.

To help assess the risk of contamination there are a range of useful websites including: the Rivers Trust who publish information on the locations of sewage discharges and overflows; the Surfers Against Sewage have a Safer Seas app which provides information on sewage discharge into the sea and some rivers; and the Government open water swimming guidance which provide relevant useful advice.

Coastal waters are tested by the Environment Agency and inland waters often by local councils, you can also test the waters yourself as rapid open water field testing kits are available. Any testing should be done following the manufacturers instructions and can help inform your risk assessment. Many manufacturers of such tests provide clear advice for their users on suitable water quality levels for different activities.

With all water use common sense preventative measures such as those advised for Weil’s Disease and blue-green algae should be always adopted and anyone who comes into contact with suspected contaminated water should wash immediately and seek medical advice if there are any health concerns.

The commonest illness associated with water sports is mild gastro intestinal disturbance (tummy upset) which can occasionally lead to diarrhoea and vomiting. When this happens you are advised to consult a doctor. Flu like symptoms and mild respiratory symptoms may also occur, as well as eye and ear symptoms. Those generally resolve rapidly without treatment.

This is a parasite infection which is widespread in the United Kingdom. Enhanced personal hygiene should be encouraged at all times. The symptoms are an acute diarrhoea illness, commonly of two to three weeks duration from which the patient recovers fully unless there are underlying conditions.

Weil's Disease is most commonly contracted from interacting with contaminated water and wet river banks, where various animals and rodents who carry these bacteria live. Good hygiene arrangements following water activities can prevent this from being contracted. Full details of symptoms and treatment can be found on the NHS website.

Certain species of the blue-green algae can produce toxins which, upon contact, may cause a number of conditions such as dermatitis, asthma, eye irritation, rashes, blistering of the skin around the mouth and nose, nausea, gastroenteritis, muscle cramps, headaches and pneumonia in some people.

Situations where recreational water users are at most risk from toxins are:

  • Ingestion of scum on water including drinking raw water or inadequately treated water.
  • Skin contact with scum or water or raw water.

Many areas of water, particularly those used by sailing clubs, will now display information about blue green algae and where high levels of blue green algae are found, a flag will be flown to warn the public. The flag will be half blue and green with the word toxic across it. For other water areas contact your local river authorities or water company to find out whether blue-green algae is present.

Hepatitis A is a virus infection of the liver which can vary from a mild or in-apparent illness to, rarely, a severe disabling disease lasting several months. Infection has been caused by swallowing water during water sports.

The incubation period varies from two to six months after swallowing the virus. The onset of the illness is abrupt, with loss of appetite, fever, nausea, and abdominal discomfort, following within a few days by jaundice. If you become ill at any time with these symptoms, call your doctor and tell him you participate in water sports.

More information available from the NHS.