You must have an automatic storage table space that was created with DB2 Version 9.7 or later. Reclaimable storage is not available in table spaces created with earlier versions of the DB2 product. You can see which table spaces in a database support reclaimable storage using the MON_GET_TABLESPACE table function.

To lower the high water mark and reduce the container size with DMS table space is a two-step operation. First, lower the high water mark through extent movement with the following statement:

   ALTER TABLESPACE TS LOWER HIGH WATER MARK

Next, you would reduce the size of tablespace

  ALTER TABLESPACE TS REDUCE

Use the function MON_GET_TABLESPACE and check on column reclaimable_space_enabled if you can reclain your tablespace.