How would your sim live, like what would you put in the house and help fill their needs? Example; Cooking Lights Entertainment Etc... I know the waterfall and swimming in the beach fills hyg...
I've built an entire house to be livable off the grid and it works really well (gallery name: Conservationist Hideaway). As long as you're not putting leftovers away, the fridge will not have food rot so you can use it to get ingredients out of it and cook them. Fresh ingredients that are grown in the garden will not rot in an off the grid fridge but fish will.