And climate changes blamed on global warming are allowing the mosquitoes which carry malaria and other tropical diseases such as dengue fever to breed further north than before.

London is hosting a WHO Environment and Health conference, and the threat posed to Europe by the rise in water-borne diseases is high on the agenda.

It estimates that one in seven people in Europe now do not have safe water to drink.

A spokesman said: "Cholera, typhoid are often associated with developing countries or perhaps medieval Europe.

"Yet these diseases are making a comeback in some European countries."

Typhoid outbreak reported

In the past few months there has been a report of a typhoid outbreak in Russia after sewage leaked into drinking water, and in Albania, 25 people died of cholera in 1994 after drinking contaminated water.

In Latvia, says the WHO, more than half of water samples from shallow wells fail to meet microbiological standards, yet half the rural population relies on these.

Kaj Barlund, director of the Environment and Human Settlements Division of the United Nations Economic Commission for Europe said: "Access to safe drinking water cannot be taken for granted, especially not in Eastern Europe."

Both Cholera and Typhoid are passed between humans by bacteria in excrement.

These are a common cause of infant death and childhood illness in Eastern European countries, as they can cause severe dehydration through diarrhoea and vomiting.

New threat from Malaria

Drugs such as Larium are used to protect travellers from malaria

The scourge of Malaria, once confined to far hotter parts of the world, is begining to have an impact in Europe, says the WHO.

Milder winters mean the mosquitoes which carry the disease, and also those which carry Dengue Fever, can breed and survive far further north than in the past.

The disease is being developed occasionally in Turkey and the southern part of the former USSR.

Dr Gro Harlem Brundtland, the WHO's Director General, said: "We can increasingly clearly see the profound changes that climate change will have for public health and for the world economy.

"The need for early warning public health systems is clear."