The order of fetching water is: Xiaoyan → Xiaoping → Xiaohua → Xiaohong;
At this point, the total time they wait is:
1×4+3×3+4×2+5× 1,
=4+9+8+5,
=26 (minutes);
Answer: When the order of fetching water is Xiaoyan, Xiaoping, Xiaohua and Xiaohong, the total waiting time of the four students is the least, which is 26 minutes.