This type of bottle is often BPA-Free and more commonly uses carbon (activated charcoal) filtration. UV light can also be used to purify water. UV filtration bottles are popular and convenient for those who are traveling to areas where water quality may be harmful, or where bottled water is not readily available. UV is effective against all water-borne pathogens. Carbon filtration bottles will eliminate some organic chemicals and improve the taste and odor of water. Carbon filtration will not eliminate pathogens, metals or nitrates from water. Carbon filters must be changed regularly to maintain effectiveness. Connected devices collect data related to a person's water intake. The data is transmitted to a smartphone, which enables tracking of an individual's water intake and alerts the user when they are not properly hydrated. These devices are a result of recent technology advancements which fall in the broader category of the Internet of Things. Devices that monitor and collect data related to one's personal health are also part of the quantified self movement. While several concepts have been introduced, none are currently available commercially. Hydration reservoirs, also known as hydration bladders, are large-volume, flexible bags typically carried in a backpack system. Users access water via a sipping tube. This system allows the user to remain engaged in activity without having to stop and unscrew a water bottle. Such reservoirs also permit the carrying of a larger water supply (thus a longer hike), as they have both more capacity and better integration into the carrying equipment than an external water bottle or canteen attached to the pack or belt. Due to growing concern over the environmental impact and cost of disposable plastic water bottles, more people are choosing to fill multi-use water bottles. However, the popularity and availability of disposable plastic water bottles continues to rise. In 2007, Americans consumed 50 billion single-serve bottles of water. Since 2001, the sale of single-serve bottled water has fluctuated by 70 percent, and this trend is continuing. In 2016, a trend among Americans called "water bottle flipping" attracted media attention. This trend has since died out and other trends are taking its place. Chemicals used for making some types of bottles have been shown to be detrimental to the health of humans. Inhalation of chemicals used in the manufacture of plastics is a hazard for the factory workers who handle the material. In many developing countries, plastic waste is burned rather than recycled or deposited in landfills. Rural residents of developing countries who burn plastic as a disposal method are not protected from the chemical inhalation hazards associated with this practice.