Why no suction pump can lift water higher than about 10 metres
Air pushes down with the weight of about 1.03 kg on every square centimetre at sea level. That load equals a freshwater column roughly 10.3 m tall, which sets a hard ceiling: however strong the pump, suction alone cannot raise water beyond that height under normal conditions.
Air pressure is essentially the weight of all the air stacked above a point, so it falls as you climb; near sea level it drops about 12 hPa for every 100 metres. The standard atmosphere, roughly the average at sea level, is defined as 101.325 kPa, the same as 760 torr or about 14.7 psi. Averaged across actual terrain, surface pressure on Earth is lower, about 985 hPa, because so much land sits above the sea.
The same 10.3 m figure explains why a diver at that depth feels about 2 atmospheres: one from the air, one from the water. Lower pressure also lowers the boiling point, which is why high-altitude cooking needs adjusted recipes or a pressure cooker. In the mid-19th century explorers turned that around, estimating their elevation by checking the temperature at which water boiled.
Barometers proved even better for surveying. In 1774 Nevil Maskelyne tested Newton's theory of gravitation on Schiehallion in Scotland and needed precise heights on its slopes. William Roy checked those heights with barometric readings and matched them to within one metre, and the technique became a standard tool of map making.
The extremes are striking. The Siberian High often tops 1,050 hPa, and Tosontsengel in Mongolia logged 1,084.8 hPa on 19 December 2001, the highest reading ever taken at a station above 750 metres. At the Dead Sea, 430 metres below sea level, typical pressure is around 1,065 hPa. At the other end, reconnaissance aircraft measured 870 hPa inside Typhoon Tip over the western Pacific on 12 October 1979, the lowest ever recorded outside a tornado. Even calm days carry a rhythm: in the tropics, atmospheric tides push pressure up and down by a few hectopascals on 12 and 24 hour cycles.
Source: Atmospheric pressure
