1 cup water
1 cup liquid castile soap
2 tsp jojoba or grapeseed oil (optional, see below)
1/8 cup aloe vera gel (optional)
5 drops of essential oil of your choice (optional)
Combine all ingredients and put into an old shampoo bottle.
Shake before use and apply directly to your scalp, since it tends to be watery.
You only need a small amount because it lathers up like crazy once you start rubbing your hair.
If your hair is curly or otherwise drier than most types, you can add some aloe vera gel for added moisture. If your hair tends to be oily, try adding a few drops of lavender or tea tree oil as both are antiseptics and add a little jump to your morning shower.