QUESTION: Should softened water be used for watering house plants or for watering the garden or lawn?

ANSWER: If the hardness of your water is moderate or minimal (10 g.p.g. or less) the sodium concentration would not likely be significant enough to harm your household plants.
Using softened water to water your outside garden and lawn is first and foremost, wasteful. Again, if water hardness is moderate to minimal, your softened water will not damage your grass and garden.

F.Y.I..... Ask your Water Softener Installer to by-pass your hose outlet.