New York's wooden rooftop tanks seal themselves without any glue
The wooden water tanks perched on New York rooftops use no sealant at all. When first filled, they leak through the gaps between staves. Within a while the soaked wood swells, the cracks close, and the tank becomes watertight, a trick inherited from the barrel makers who first built them.
As Manhattan buildings rose in the 19th century, coopers turned their craft to a new market. For a long time the city required a rooftop tank on every building taller than six storeys, and two family firms dating from that era still build them. Steel cables or straps bind the staves. A typical tank holds 250,000 to 500,000 litres; daily supplies are drawn from the upper portion while the bottom layer stays in reserve for firefighting. A float valve or switch triggers a pump to refill it when the level falls. Some owners hide the tanks behind ornate brick enclosures; others leave them exposed on bare frames.
Height is the whole point. Every 102 millimetres of elevation adds one kilopascal of pressure, so a column 30 metres tall delivers roughly 300 kilopascals, enough for most household needs. A standard municipal tower stands about 40 metres high and is usually built of steel or reinforced concrete, with an inner coating to protect the water.
Towers smooth out demand. Levels drop during busy daytime hours and pumps refill them overnight, which means pumps can be sized for average rather than peak use, saving on electricity and complex controls. The constant draining and refilling also keeps the water from freezing. Because gravity supplies the pressure, water keeps flowing during a power cut, though only until the tank empties.
Modern pressurised networks took shape in the mid-19th century with steam pumping and stronger pipes. British engineers first used tall standpipes to even out the pulsing flow from steam engines, and these later gained storage tanks. Railways built towers so steam locomotives could take on water every 11 to 16 kilometres, and in California, enclosed tankhouses supplied individual homes from the 1850s to the 1930s.
Source: Water tower
