I had a brainwave recently about the water left in the steamer after steaming vegetables. It is always a bit yellow, greenish or purplish, depending on what was steamed. So I thought, why not use that on plants. As whatever has leached into steamer water came from veg, it probably is beneficial to veg.
Now I use it for watering or put it into the kitchen waste bin to go to the compost heap. Adding extra moisture to the bin has had the effect of faster rotting and the plants are not looking bad either, although they also get normal fertiliser, so I cannot say how effective steamer water is.