That's ok in an emergency, but not recommended for long term use. The minerals in fresh stream water, or even tap water will build up in an engine, radiator and the heater core, causing trouble down the road. Use tap water at a minimum, or distilled or deionised water at best, with something in the mix for a lubrication for the water pump and as a corrosion inhibitor. Ethylene Glycol, Propylene Glycol, or a Carboxolate antifreeze at a rate of 25% will help, perferably at 50/50, or a specialised water soluble oil made just for this specific purpose at a minimum, providing you NEVER see freezing temps.
Not only does antifreeze/coolant help with lubricating and corrosion resistance, it also helps cool the engine more efficiently, due to the passivating qualities of the product itself. Just trust me on this one, seeing as I've been at it for over 30 years. Also with the number of "new" coolants on the market, and owning antiques, modern North American and European vehicles, I've done a lot of research on this topic.
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