In a pressure cooker combine water and garbanzo beans.
Bring to boil and reduce heat to low simmer for 3 hours.
Beans should be very soft and slightly caramelized at the end of the cooking, but you should have some remaining liquid to be used later.
When done, let cool until beans are warm before blending.
Transfer the beans and remaining liquid to a food processor.
Add lemon juice, salt, cumin and garlic and blend until smooth.
Last, add tahini paste and blend until thickened.
Hummus has a tendency to thicken up even more as it cools; you may thin it later with water if you desire..