Cut the stem off pumpkin. Cut pumpkin half and scoop out the inside flesh and seeds (save seeds for another use!) Cut pumpkin into quarters and rub each piece with olive oil. Place quarters cut side-down in a greased baking pan.
Roast pumpkin at 350F 45-50 minutes or until very fork-tender. Once pumpkin is cool enough to handle, peel the skin off and discard. Place pumpkin in a blender and add water. Blend pumpkin on high speed until completely smooth and pureed.
Allow pumpkin puree to cool slightly before transferring to an airtight container to refrigerate.
Pumpkin puree may be refrigerated up to 1 week. Pumpkin puree may also be frozen up to 3 months.