Because the bottle sealed from atmosphere and because that the pump inlet pipe( pipe B ) is above the water surface , a negative pressure (vacuum ) will be occur above the water surface (below the atmospheric pressure) during pump operation , and the pressure within the water (inside the water) will be atmospheric pressure due to that one end of pipe A has been immersed below the water surface and the other end open to atmosphere , this causes that the water at the surface to be evaporated and the minimum pressure occurs inside the bottle is the water vapor pressure (corresponding to the temperature within the bottle
This will cause the water level inside the bottle to be below the distance of the end of tube A (below 0.15 m of the original water surface ) and then no more evaporation happened and the pressure inside the bottle will rises to the atmospheric pressure