After you boil water to make the boiled water sterile the sterile water after you boil it will keep sterile in the fridge for up to 24 hours.
After 24 hours the boiled water in the fridge is no longer considered sterile so you'd need to boil the water again and let it cool down and then refrigerate it again or use it before 24 hours.
A friend of mine who is a neonatal nurse says that when you put sterile water in the fridge it will keep for 24 hours so it's best to use the water within 24 hours.
Then if you need to sterilize it again if you need sterile water.
As long as the water has remained in a sealed sterile bottle the water should still be sterile enough to use it even after 24 hours which is what I think.
But the nurse said that after 24 hours it's no longer sterile.
But I used sterile water for my babies after 24 hours in the fridge and they turned out okay.