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 and also you should have some remaining liquid to be used later (see Cook's Note below).
When done, let cool until beans are warm before blending.
Transfer the beans (and the remaining liquid), lemon juice, salt, cumin and garlic to a food processor and blend until smooth.
Add Tahini paste and blend until flavored and thickened. (Hummus has a tendency to thicken up as it cools and water can be added later if desired.)
Cook’s note: The remaining water at the end of the cooking should be reduced to about 1/3 inch below top of the beans. If more water remains, then cook uncovered until water reduces.