okay, there are few things you need to check.
1: check if your car's cooling fan is working properly, spinning at full speed or not ?
2: change your radiator cap. worn out radiator cap can also cause loss of radiator water and heating up of engine.
3. Check if car is reducing water ? If yes, check all the hoses and pipes, is there any leak or radiator cap is faulty.
4. i doubt that radiator is not properly serviced. where did you get it serviced from?
My Swift was heating up and reducing water,
it ended up that radiator cap was faulty and there was a minor leak underneath the radiator pan.
mechanic did a good job and gave me guarantee of his job, he changed the cap and cleaned radiator and then changed upper and lower pans of radiator as well. Alhamdulillah I took car Lahore - Sialkot, and Lahore - Sheikhupura ... water level is intact, car is not heating up , so i am happy with his job.
which city you are in ?