What happens if i add water to my Toyota innova e coolant reservoir?

Answer 1

You will dilute the mixture. You should add a mix of 50% straight antifreeze and 50% clean water. This mixture will protect the system from freezing down to -34 degrees F.

Answer 2

Then the coolant mixture will become slightly more diluted. So long as the majority of what's in the cooling system is antifreeze, you'll be fine. It may lower your freeze point, though.