Negative pressure device for water supply

The utility model provides a negative pressure device for water supply, in order to solve air pollution on various upending-type water supply devices. The concrete proposal is that a water storage bag similar to outline of the barrel container is arranged in a barrel container. Opening of the bag can be stretched outside the mouth of the barrel container. A cap of the barrel container can seal the opening of the bag. Air vents are positioned on bottom of the barrel container. When the barrel container is upside down, air pressure will go into the barrel container through air vents so that water flows water dispenser for drinking under pressure. Air can not go into the water storage bag to pollute the water and the remnant water in the barrel. Moreover, one can change water storage bag after every time the water is changed, so that potential pollution from the container is avoided. The utility model can as well apply to hanging saline bottle in medical intravenous instillation area.