There are two cases to consider: 1- If you have just purchased your Berkey water purifier and the filters are new, the problem is usually due to high water stress. This prevents air from being purged from the micropores of your Black Berkey water filters. It is imperative that your filter elements be purged of this air to allow water to pass through them. A beige priming washer and priming instructions are included with Black Berkey elements. Remove your filters, prime them, then reinstall them in your unit. This should solve the slow flow problem. 2- If the flow rate slows significantly during the use of your Berkey system, the problem can be easily solved by cleaning the elements again. Turbidity and sediment clogging of the micropores are usually the cause of this problem. Simply remove the elements from your system and scrub the outside of each element with a Scotch Brite pad or stiff toothbrush. Scrub one part of the element until you see some black appear on the sponge or toothbrush, then move to another part until you have gone around each element. This simple process should only take a few minutes. Reboot each element, then reinstall them in your device. Your flow should be restored.
WARNING: Never use soap or detergent.