(1) Let the analytical formula of water storage amount y and water discharge time x be y=kx+b,

Substitute (2,17) and (12,8) into y=kx+b,

get 17 = 2k+b8 = 12k+b,

get k =-.

(2) According to the figure, the water intake of each student is 1.25 liters,

the first (22-4) students need to receive 1.25×18=4.5 liters,

the water storage capacity y=18-1-4.5=12.5 liters, and

∵ two water pipes are simultaneously. 812? 2=1.9,

∴4.51.9=5,

∴ It takes 5+2=7 minutes for the first 22 students to receive water.

(3) When x=11, according to (2), four students will be picked up in the first two minutes, leaving the water storage capacity of the drinking machine for eight minutes.

The water flow of the drinking machine in these eight minutes is: 8×1.9=7.2 liters,

7.21.25=28.8,

.