Water (H2O) is a chemical compound whose molecule contains two atoms of hydrogen and one atom of oxygen. It's a colourless fluid without taste or smell. It appears in three states of matter: solid, fluid and gas. Physical, biological, radiological and chemical characteristics of water affect its quality. Constant circulation of water in nature is a process that makes life on Earth possible. Most common water pollutants are waste waters, nuclear facilities, pesticides etc. Water is usually drained from water supply systems in every household, but it needs to go through different sorts of treatments before it's clean and ready to drink. Another source of water is bottled water that can be bought in almost every store. It is extremely important to keep the drinking water clean, and healthy because contaminated water can be very dangerous for human health. Water is the most abundant element in the body structure of every living thing. There is no life without water. Water is a cure because of its medical benefits that positively affect different sorts of diseases. Water is a medium where all the processes of organism necessary for living take place. Water is extremely important for a lot of different functions of human body. Adults and children lose water from their body system through different body processes, so it is very important for everyone to drink water to prevent dehydration which could cause serious consequences bad for health. Adults and children should drink proper amount of water determined by age, sex, weight, climate conditions etc.