Hi Natylesca.
The reference to water is a very interesting issue that you have touched, and I mean the liquid that you are putting the cooling system.
As you know, there are several types or classifications of water, according to their sources. There are harder, soft waters, etc. A hard water is what is considered to have more lime and other elements that make it more difficult to treat, it requires more treatments so that some materials do not damage much.
Soft waters are somewhat more pure, loss of lime and other heavy substances.
In some countries, hard water, which usually contains high percentages of lime, forms a whitish scab in the cooling ducts of cars engines, which obstructs (it is like cholesterol in the veins) the ducts. For this it is necessary to clean the systems. But even better, it is not to use common tap water because it is usually very harmful to the ducts. I corrode, the pica, cavitation problems in the water pumps, etc.
It is very possible that the origin of your problem is even: tap water.