Softened water is treated with salt to help remove the minerals from hard water. ... It's unlikely that your water softener salt will kill your grass, especially not by using it to water occasionally. But prolonged use of soft water just isn't ideal for your garden.

Can I use softened water on my lawn?

Softened water is therefore high in sodium and is not the best water to use for irrigating lawns and gardens because it can cause salt buildup on the soil surface.

What happens if you water your lawn with softened water?

Soft Water's Impact on Your Lawn

Since soft water contains plenty of sodium, its regular use can lead to spotty or absent growth. The negative impact of watering with this kind of water reaches its highest levels in areas with little rainfall.