You may use 洗脚 side for 洗菜, and 洗菜 for 洗脚 from time to time.
On the other hand, water in remote region is priceless, and it does not matter how to use. You would cook other than feet washing firstly, which could make right order.
Tank water at Coxs River campsite is not recommended for drinking, but ......
Water from Coxs River is drinkable and especially for tea or hot pot.