In an emergency as long as it's not freezing out the water is fine to use as a coolant in your engine.
However water will freeze unlike antifreeze.
Using water in a coolant system on your car or vehicle in place of coolant during an emergency is perfectly fine.
The water will cool the engine down just as good as the engine coolant will and it will allow you to get home or to a shop to have the coolant leak fixed.
However long term use of water instead of coolant in your vehicles coolant system can lead to rust buildup in the engine as well as the radiator and water pump.
That can lead to the water pump eventually failing and your radiator becoming clogged due to the rust.
So when you get to where you're going you need to fix the coolant leak and then drain the water out and add the coolant to prevent the engine from rusting out inside.
The coolant will also protect your engine from freezing during the winter as well.
So you do not want to run water in your engine during winter because it can and will freeze the engine block which then leads to the engine cracking and then you'll need a new engine.
So water is okay to use as engine coolant in an emergency situation but replace it with engine coolant as soon as possible.