Misting can be a good way to keep the leaves hydrated but not too soggy. Always make sure that there's good drainage to prevent root rot. The plant can be sensitive to fluoride, which is often common in the public water supply, and this species does not tolerate hard water, especially if it's in its growing stages.
Use a watering can or a sprinkler with purified or distilled water. Make sure to evenly water the entire surface of the soil so the stems won't rot. Use distilled water from time to time to avoid the death of the plant, leaf burn, or stunted growth instead of tap water. Another option is to utilize rainwater whenever it's available. Keep the soil moist every time but prevent it from being too soggy if the Rainbow tree is planted in a pot.
If it's outside planted in your garden, you need to have proper drainage and allow the soil to dry completely before you turn on the sprinkler or the garden hose, as this can lead to root rot and yellowing leaves.
Some use hydrogen peroxide as a treatment in the water, but this is not recommended for regular use. The hydrogen peroxide will stimulate rainwater but only do this occasionally. A filtration system might also be valuable for removing nitrates, salt, and lead that might be contained in the water.