The demand for this particular group changes from being
inelastic to elastic at r =$0.93 per thousand. At a price of $1.60
per thousand the quantity purchased by the average size depart-
ment store is 60,000 gallons per month. If prices increased 25
percent to $2.00, quantity is reduced by 35 percent to 39,000.
 The relationship between quantity purchased and size of de-
partment stores is also illustrated. The quantity of water pur-
chased is inelastic with respect to a change in the size of store.
Given r=$0.40, the quantity purchased by the average depart-
ment store shown is 218,000 gallons per month as compared to
343,000 gallons per month for the largest store (Figure 1).
Thus, doubling store size leads to a less than doubling in the
quantity of water purchased. An increase in the store size from
the average of 65,000 square feet (A=650), to a store size of
130,000 square feet. gives a 57 percent increase in purchases of
water.
 The nature of the price responsiveness is also of interest in


0.40


=650 (average size store)

A=1300


 100 200 300 400
 Thousands of gallons per month (W)

Figure 1. Monthly water demand by department stores of different
 sizes (A=hundreds of square feet, floor space), Dade and
 Monroe counties, 1975-1976 (data from Appendix B. Table
 1).