At the track they use straight water to keep their engines cooler. This is not something for daily use. Guaranteed corrosion will develop. Eventually it will clog, you will need to flush out the cooling system, or even replace the radiator. Worse could happen.
You could do the same. When you head to the track put water in. And when you are done, replace it with coolant. And whatever you do, do not put in hard water. Water from the pipe is killer. Use distilled water, or even purified water.