@m.hassan.61
Using only Distilled water is not recommended, it could only be beneficial if you mix it with Concentrated radiator in 50:50 ratio or 75: 25
However, it is better to use Pre-diluted coolants like Toyota, Fuchs or Caltex.
you can do these things in Karachi:
Buy Toyota coolant from Toyota 3S dealer ship like Toyota Eastern Motors or Toyota Central Motors
Go to Buffer Zone at Khalid Radiator service or any place convenient to you for Radiator service (There must be much amount of rust there due to prolonged usage of plain water
After radiator flush, pour Toyota Coolant in it