Radiator coolant is a mix of anti-freeze and water. As there is no risk of temperatures in Doha falling below 0, it is safe to keep using distilled water for your radiator.

But if it is empty within just 2 days, you have a serious leak. Get the mechanic to do a pressure test to try and find the leak.

Either you can put in a leak sealant which will hopefully block up the hole, or worst case is you need to replace the radiator.