Travellers will be familiar with the request displayed in many hotel bathrooms to re-use towels for the benefit of the environment. They may be less aware of the scale of measures being taken by some hotel chains to improve their green credentials and of the impact such a simple action can have on water use.
InterContinental Hotels calculates that its towel re-use programme saves 199 million litres of water a year in the US alone. Marriott International, with 3,200 hotels worldwide, reckons its linen re-use programme saves 11-17 per cent on its water and water treatment costs.
As well as urging guests to re-use towels, some hotel chains urge customers not to demand fresh bed linen every day.
Lower water use can have knock-on effects by cutting energy used to power washers and dryers and reducing the quantity of detergents needed. Marriott says that laundry savings at its central European hotels has reduced phosphate discharge into the waste water system by 100,000 kilograms.
The attentions of regulators and green activists may have focused on other aspects of the tourism industry — notably aviation — but hotels are well-placed to make a contribution to reducing environmental damage.
More than 900 million international tourists travelled in 2007 and the United Nations World Tourism Organisation forecasts 1.6 billion tourists by 2020.
When they reach their destination, travellers are more profligate in their use of water than the local population.
A survey of water consumption on the Spanish island of Mallorca in 1994 showed that while a country dweller consumed 140 litres of water a day and a city dweller 250 litres, the average tourist used 440 litres and a luxury golf resort 880 litres for each visitor.
For hotel managements, water issues can do more than influence their premises' appeal to guests. In extreme cases, they can determine the hotel's very survival. In many developing countries, the water infrastructure may not be highly developed.
A large hotel may have difficulty obtaining adequate and regular supplies or may only achieve it by depriving the local residents and farmers.
Imagine having to tell your guests that they can only shower every other day, that supplies of bottled water have become hard to obtain and that providing clean laundry has become impossible, suggested Green Hotelier, the magazine of the International Tourism Partnership (ITP), a business group that promotes environmental and social responsibility.
"It is not as unlikely as may seem," the magazine explained. "Puerto Rico and St Lucia experienced dry spells in 1995, resulting in cancellations and hotel guests cutting short their holidays. Some resorts were even forced to close their doors."
Waste water can also pose a serious threat to a hotel business. Stomach upsets, vomiting and ear and skin infections can result from swimming in polluted water. Discharge of improperly treated waste water into the sea can lead to algal outbreaks and damage coral reefs.
Tour operators often check a hotel's fresh and waste water management processes as a part of their contract. Hotels put water to a wide of range of uses, with only 5 per cent estimated to go to drinking and cleaning food.
Some goes to guests taking showers and washing; some to irrigating gardens and golf courses; filling swimming pools and jacuzzis; cooling and decorative use such as fountains; and irrigating land used to produce food for tourists. Water accounts for 15 per cent of the total utility bill of many hotels.
For many travellers a hotel stay is a luxury experience. They might scrimp at home but they do not want to do so on holiday. This puts the onus on the hotel operator to take initiatives that will save water without obviously impinging on the pleasure of the stay.
De Vere Venues, the conference arm of the De Vere hotel group, is testing devices installed in the pipework to showers in its 3,310 rooms to add air to the water. The strength of the flow is maintained but water use is reduced.
It is also introducing "liquid pool covers" in its seven swimming pools. These are unnoticeable to the swimmer but when the water surface is still the molecules form an invisible surface on the pool that retains heat and prevents evaporation.
"We are also in the throes of a water scanning project to detect leaks because a lot our premises are old," says David Greenhill, head of health and safety. "But this involves capital investment and we are progressing slowly, given the current financial climate."
"Water management is a huge issue for the industry," says Stephen Farrant, director of the ITP. "Some of the more enlightened companies have focused on it but there is huge scope to do more."