It will last a lot longer if you get another DI vessel. My TDS is around 57 so much the same as yours. You have two vessels, vessel A and vessel B. Connect vessel A to your tap and use it until your TDS begins to rise, Then use another pipe to connect the outlet on A to the inlet of B. Say the outlet reading from A is 005ppm, your resin in B is only purifying 005ppm water instead of 60ppm from your tap. Keep an eye on the TDS reading from A, and as soon as it gets to 60ppm the same as your tap change the resin. You now have water from your tap going through vessel B first and the connected to vessel A with the new resin.
This is how using two vessels saves you loads on your resin costs. Dai