There are some brands of sparkling water which have neither sweeteners or sugars, but are infused with fruit flavours. Dash, Ugly and Aqua Libre are three brands. The Dash black currant is particularly tasty. They are worth a try for a bit of added flavour without the sweetness of sugar or sweeteners.
I do like plain water, so long as it is ice cold and drink buckets of it. After exercise or on a hot day adding the juice of half a lime and some pink Himalayan salt to a large glass of iced water is very refreshing.