Coolant for used cars

[rukmalranaweera]

I have recently bought a 2008 allion and when I checked the radiator is filled with water. They used water instead of Coolant for around 7 months. 

So is it good to flush the water and use Coolant for that car. I heard someone saying it's not good to use Coolant for water used radiators. 

Please advice. Thanks

[Hyaenidae]

I don't think 7 months of using water would cause rust that would cause clogging or leaks, just flush the radiator out and fill it with coolant