For example, the sustainable hospitality industry includes technological innovations (such as low-flush toilets and special showers to save water) and energy saving (such as special heating, ventilation and air conditioning systems). Some hotels want to transform into sustainable hotels, because many people think that the concept of sustainable development will become the development trend of the world. If guests live in the same room for a few days, hotels never wash towels and bed linen, saving energy, water and (pollution caused by) cleaning detergent. Across the hospitality industry this is probably the most commonly applied sustainable practice, with hotels placing information cards in guest rooms urging them to consider the effects of towel recycling on the environment.