Water towers come in a variety of designs and sizes. Buildings with water towers on top are a frequent sight in many cities. Tall structures in cities frequently have to deal with their own water pressure issues. Because the structures are so tall, they frequently exceed the height limit of the city's water pressure. Thus, they need to have their own source of water supply far away from the structure where it is drawn up into the tank by a pump. The design of these towers varies depending on what type of water they are storing for subsequent distribution. Some are very simple, with only one large tank inside the building's walls. This is the case for smaller tanks that are not expected to hold more than several thousand gallons of water. Larger tanks can be made out of concrete or steel and often have an elevator shaft or other means of reaching the top of the tower for maintenance work or to fill them up with extra water during heavy rainstorms. These towers are usually found in rural areas where there is no municipal water system available. People in these areas often buy water in bulk from local farmers who sell it by the gallon at a price determined by the farmer. These prices can be quite low (like $10-40 per 1000 gallons), but that also means people are going to want to waste as little of it as possible. They will often store this water in old oil tanks recycled from old cars or trucks.