Topping up coolant with tap water

[trickywoo]

Is anything really bad likely to happen if you top up coolant with tap water?

Obviously adding anti-freeze in the correct proportion.

Its a soft water area (kettle stays clean etc).

Thanks.

[HereBeMonsters]

I hope not, been doing it for years!

[Reidy10_0]

I would think a small top up would be OK.

[RDM]

Some water pumps need lubricated with some form of coolant additive at
least the book for my car says so. In saying that my car dumped it's coolant
on Friday and I'll be topping up with tap water for now until I can get the
front bumper off to see if it's a burst radiator or just a hose.
I'd check what the requirements are for your water pump before putting too much straight water in.

[Snake the Sniper]

Only ever used tap water for my cars. Not had an issue yet.

[Steve_D]

Never used anything else.
You will need to get the antifreeze right before too long as the antifreeze also contains corrosion inhibitors which most engines need.

Steve

[//j17]

If you are just topping up because it's a little low 100% tap water will be fine. Yes it will drop the coolant/water ratio but it will drop it from 33% coolant to 32.99% coolant.

Assuming you drive a modern car and it's the first time you've needed to top it up then it should be corrected by the garage at the next service.

If it's a modern car and topping up is a regular occurance...check for leaks as it shouldn't be using fluid and it has to be going somewhere (possibly bad).