It's going to depend upon the TDS content of your water, however, it's not going to last very long. This is an inefficient method for removing salt for drinking water. You need a reverse osmosis system. this will give much better performance in a much more economical way.
See this link to look at our RO units:
Reverse Osmosis Systems and RO Water Filters for RO Systems RO will remove 95+% of salt and many other contaminants for up to 3 years before the membrane needs to be changed. The carbon cartridges will require more frequent changes.
Thank you,
WaterFilters.NET