Tap water effect on plants?

Trying to keep the garden healthy and giving them a brief hand water every day in the recent heat. Noticed they're going a bit yellow after a few weeks having been so nice and green coming off winter.

I also fertilise twice a year. Not sure if this is enough? Should I switch to monthly maybe?

Not for lack of water anyway. So, I'm wondering about water composition and how it affects the garden. It's just regular tap water. Not bore. Any knowledge to share? What fertiliser and water regime keeps your garden really nice?