Human
In general, humans can survive for two to eight weeks without food, depending on stored body fat. Survival without water is usually limited to three or four days. About 36 million humans die every year from causes directly or indirectly related to starvation. Childhood malnutrition is also common and contributes to the global burden of disease. However global food distribution is not even, and obesity among some human populations has increased rapidly, leading to health complications and increased mortality in some developed, and a few developing countries. Worldwide over one billion people are obese, while in the United States 35% of people are obese, leading to this being described as an "obesity epidemic." Obesity is caused by consuming more calories than are expended, so excessive weight gain is usually caused by an energy-dense diet.
Water scarcity in Africa
The most immediately apparent impact of water scarcity in Africa is on the continent's health. With a complete lack of water, humans can only live up to 3 to 5 days on average. This often forces those living in water deprived regions to turn to unsafe water resources, which, according to the World Health Organization, contributes to the spread of waterborne diseases including typhoid fever, cholera, dysentery and diarrhea, and to the spread of diseases such as malaria whose vectors rely on such water resources, and can lead to diseases such as trachoma, plague, and typhus. Additionally, water scarcity causes many people to store water within the household, which increases the risk of household water contamination and incidents of malaria and dengue fever spread by mosquitoes. These waterborne diseases are not usually found in developed countries because of sophisticated water treatment systems that filter and chlorinate water, but for those living with less developed or non-existent water infrastructure, natural, untreated water sources often contain tiny disease-carrying worms and bacteria. Although many of these waterborne sicknesses are treatable and preventable, they are nonetheless one of the leading causes of disease and death in the world. Globally, 2.2 million people die each year from diarrhea-related disease, and at any given time fifty percent of all hospital beds in the world are occupied by patients suffering from water-related diseases. Infants and children are especially susceptible to these diseases because of their young immune systems, which lends to elevated infant mortality rates in many regions of Africa. Water scarcity has a big impact on hygiene.