The density of the air in the right leg decreases. The air pressure decreases. The water accelerates towards the right. You can then support a column of water 10.3m high. So a column of water 10.3m high will exert a pressure of 101kPa .
Many pumps operate on the simple principle of pushing and sucking.
However, you can never suck water out of a well, when the water level is more than 10m below the pump. In a vertical, water-filled pipe gravity creates a pressure gradient in the water. The water below has to support the weight of the water above. The pressure exerted by 10m or 33 feet of water overhead is equal to the atmospheric pressure at sea level. One way of maintaining pressure in plumbing is to have tall columns of water connected to the pipes.