The Long Man's Pillow question

Imagine you're living in a time of drought. You own a well that produces enough water to quench the thirst of 20 people per day. There are 20 people in your town, including you. There are also 30 strangers who have wandered into town, all of whom are dying of thirst. There are no other water sources within a hundred miles. How do you decide who gets to drink?