The night before making the hummus, put the chickpeas in a large bowl and cover them with twice their volume of cold water. Cover the bowl and let them soak overnight.
To make the hummus, drain the chickpeas and rinse them with fresh water. Put a medium pot over high heat and add the chickpeas and baking soda. Cook for about 3 minutes, stirring constantly. The baking soda and the stirring helps loosen the skins of the chickpeas which means you don't have to peel them. Which I wouldn't do anyway!
Add the 6½ cups of water and bring to a boil. Skim off any foam or skins that rise to the top. Turn the heat to medium and continue cooking until the chickpeas are tender, mashing easily between your fingers or under a spoon, but not too mushy. This can take 20-40 minutes depending on the type of chickpea and the freshness. Continue to skim the foam as necessary.
Drain the chickpeas and put them in the bowl of a food processor. Process until you get a stiff paste.
With the machine running, add the tahini paste, lemon juice, garlic, and salt (start with 1-2 teaspoons and add more as you taste).
Slowly drizzle in the iced water and allow it to mix for about 5 minutes until the texture is very smooth and creamy.
Transfer to a bowl, cover the surface with plastic wrap, and let it rest for 30 minutes. Serve right away or refrigerate. Remove the hummus from the fridge at least 30 minutes before serving.
To serve, spread it on a plate or platter, drizzle it with a good olive oil, and sprinkle it with cumin, paprika, and/or red pepper flakes. Eat it with pita or bread, or an assortment of freshly cut vegetables, especially cucumbers and tomatoes.