No.
No, we do not recommend using softened water with the Black Berkey filters, this improper use of the Berkey Filters will result in a void of the 2-year pro-rated filter warranty.
The Berkey purification elements are designed to remove heavy metals, but will not altogether remove mineral salts, which are added by a water softener. The salt added by a water softener, embeds in the exterior of the filter, requiring frequent cleaning. With each cleaning the clogged exterior of the filter is removed, so water may pass through again. For this reason, these salts tend to shorten the life of the filters.
If you do have a water softener, you can use a Berkey IF you bypass the softener to get your drinking water. Most water softeners have a bypass valve or a way to get water before it passes through your softener. Therefore, we highly recommend obtaining pre-softened water directly from the source rather than running softened water through your Black Berkey Filter Elements. If you cannot do so, the maintenance and replacement frequency of the elements may increase.