In a medium bowl, pour ½ cup of cold water.
Add garlic powder, turmeric, za'atar, salt, one tablespoon of lemon juice, and whisk.
Add the tahini. Using a whisk or a fork, mix until thoroughly blended. Taste and adjust for taste if necessary.
Slowly add more cold water, two tablespoons at a time, whisking after each addition until smooth.
Keep adding water slowly until the sauce can drizzle from a spoon.
Keep refrigerated for up to a week. If you like, you can splash in a little extra water, to your taste.