Water is the same. Any water left in a glass or cup by my children gets used for the cats or plants. When we steam, or even boil vegetables, I can't stand to see so much water poured down the drain, so instead, I water my plants with the cooled water that remains.
It is an excellent source of nutrients for your plants! It also leaves me feeling less guilty about using more water in one pot of vegetables than some people have access to in a week.
In summation, today's tip is: Use your leftover water from steaming or boiling vegetables to water the plants!