The average monthly water savings of Grandma Zhang’s family:
39.6÷6=6.6 (yuan),
The average monthly water savings of Grandma Li’s family Fee:
24÷3=8 (yuan),
6.6 yuan; 8 yuan,
So the average monthly water bill saved by Grandma Li’s family A lot,
Answer: Grandma Li’s family saves a lot of water on average every month.