Thank you for contacting ZeroWater. Sometimes the filters will develop an air pocket inside them. This can happen as the filter contents settle in transit or during the filtration process as air bubbles can become trapped inside of the filter. Then once the water level in the pitcher meets the air pocket it can stop or severely slow down the flow of water through the filter due to the pressure of the water both above and below the air pocket inside the filter. First try unscrewing the filter, then re-installing it. If that does not work to alleviate this, it is best to lift the filter and reservoir out of the pitcher or dispenser and tap the side of the filter using moderate force to help break up the air pocket. Then take just the filter & reservoir to the sink and put about an inch of water into the reservoir and allow that to run through the filter and right into the sink to displace and dispel the air pocket. After that has completed then return the filter and reservoir to the pitcher or dispenser and continue to filter water as normal.
If this does not solve your issue please contact our customer support team at 1-800-503-2939 option 2. We are available Monday through Friday, 8 AM to 8 PM CST.