If you've boiled or flash-cooked a large pot of vegetables, don't toss the leftover water down the drain. Instead, let the water cool and give your houseplants or garden a nutritionally packed treat to help them thrive. The residual vitamins that come from the vegetables are incredibly beneficial for plants. Just make sure the water is completely cooled and free of any salt, which is dehydrating and damaging to plants. If there are bits of cooked vegetables in the water, strain them out before using the water for your plants.