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PatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.

This is increased plasma volume, leading to low haematocrit and hyponatraemia.

Water intoxication can arise from:

  • Administration of too much intravenous fluid.
  • Ingestion of too much water, especially if electrolyte levels are depleted.

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Haemodilution occurs physiologically in pregnancy. This may result in lower haemoglobin concentrations than in the non-pregnant state. However, many women function well and do not require iron supplementation. It is common in chronic heart failure, where it may contribute to poor outcome.[1] At-risk groups for water intoxication include:

  • Infants under 1 year old.
  • Athletes - eg, marathon runners/extreme athletes and hikers who drink excessively during prolonged exertion.[2][3]
  • Also associated with the use of methylenedioxymethamfetamine (MDMA, or 'ecstasy') with prolonged dancing and high water intake at raves/events.[4]
  • The mentally ill, in association with polydipsia.


  • Confusion
  • Nausea/vomiting
  • Seizures
  • Coma

It may be fatal.


Brain oedema.

Treat the underlying cause. Correct electrolyte balance in severe cases of water intoxication. Fkuid restriction may be considered in chronic heart failure.



  • Acute normovolaemic haemodilution (ANH) may be used in operations where there is a large anticipated blood loss. It involves removing some of a patient's own blood and replacing it with fluids, to maintain normal volume. This process ensures that the blood that is lost during the operation is diluted, ie fewer red blood cells are in it. This reduces the load on the heart and allows the blood to flow more easily through the capillaries. The patient's own blood is returned after the operation.
  • Haemodilution improves the flow properties of the blood so that, theoretically, oxygen and nutrient supply to the brain is improved (eg, after a cerebrovascular event) and damaged brain cells may survive. This treatment had been shown to reduce brain infarct size in animals with experimental stroke and it was first tried in the 1970s. However, a recent Cochrane review of the (considerable amount of) research showed that there were no benefits from this treatment.[5][6] 

Further reading & references

  1. Androne AS, Katz SD, Lund L, et al; Hemodilution is common in patients with advanced heart failure. Circulation. 2003 Jan 21;107(2):226-9.
  2. Noakes T; Hyponatremia in distance runners: fluid and sodium balance during exercise. Curr Sports Med Rep. 2002 Aug;1(4):197-207.
  3. Noakes TD, Sharwood K, Collins M, et al; The dipsomania of great distance: water intoxication in an Ironman triathlete. Br J Sports Med. 2004 Aug;38(4):E16.
  4. Cherney DZ, Davids MR, Halperin ML; Acute hyponatraemia and 'ecstasy': insights from a quantitative and integrative analysis. QJM. 2002 Jul;95(7):475-83.
  5. Asplund K; Haemodilution for acute ischaemic stroke, Cochrane Review, October 2002
  6. Chang TS, Jensen MB; Haemodilution for acute ischaemic stroke. Cochrane Database Syst Rev. 2014 Aug 27;8:CD000103. doi: 10.1002/14651858.CD000103.pub2.

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Dr Hayley Willacy
Current Version:
Peer Reviewer:
Dr Hannah Gronow
Document ID:
2218 (v22)
Last Checked:
Next Review:

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