Herbs and Aromatics
It may sound odd, but adding herbs can offer a surprising and satisfying flavor to plain water. The most popular herb used for flavoring water is mint, but you could also try basil, thyme or lavender if you want to try something different. Other aromatics, like vegetables and spices are a great option. They offer depth of flavor to dishes and chefs use them as a base on which to build flavor.
Ginger, lemongrass, celery, and Kaffir lime leaves are examples of aromatics that would work well in infusing your water.