Other posters are spot-on in terms of it being a non-issue for the South. The more water you have, the better it will cool anyway. You want some antifreeze for lubrication and anti-corrosion purposes, but you're in good shape there with what you have.
The only thing I'd add that hasn't been covered is that under normal operation, your car doesn't "use" any coolant, so if you have to continually add coolant, you have a problem that you should look into. Could be a head gasket (coolant escaping into the oil or combustion chamber), a leak in a hose, seal, or water pump. In any case, have a look.