Sort of depends on what comes out of your tap. Softened water tends to be slightly salty, however, and that's not good for plants. Won't kill them straightaway, but isn't good in the long run. Plants don't generally care about hard water, except that hard water is often alkaline, and some plants won't tolerate that.

Softened water should not be used on plants. They work by replacing minerals like calcium with sodium or potassium.

Well, in most gardens, you don't get calcium from the water. You get it from the soil. Also, water softeners actually REPLACE both calcium and potassium with sodium. But having a little extra calcium and potassium for your plants by not softening your water isn't going to hurt. Sodium, in fact, is a mineral that is not essential for plants, unlike calcium and potassium.

I have watered indoor plants a long time with my softened water - and my garden when needed. Only in my aerograden did I maybe notice plants not doing as good. Tap water has chlorine which I would think is bad for plants?

I do know chlorine dissolves quickly. I often fill a large watering can so only 1 in 4 or 5 waterings would have any chlorine.

Tap water is usually disinfected with chloramines. Chloramines are used because they stay in the water longer than chlorines and don't disperse readily. But there is little evidence that the small amount that is used interferes with plant growth.

Thanks!

Your local water agency is required to publish a quarterly report, which is probably available online. It will tell you if they are using chlorine or chloramine in your water. The problem with softened water is not the lack of calcium, which plants get from the soil. It's the presence of sodium. If you have a water softener it is most likely attached to soften you indoor water. Your outdoor spigots wouldn't be affected because they branch off from your water supply line before the water softener.

You can use potassium chloride instead of sodium chloride as a regenerant in water softeners. What comes out will be potassium, which is helpful for plants. But potassium chloride is significantly more expensive, and I think it takes more of it to do the same job.

Thanks!

I have softened water, and I have no problem with seedlings or plants grown in the house.