Ah yes, very good observation, I had forgotten that coffee also contains caffeine which can have a diuretic effect and cause increased urination.  In that case, a good alternative would be herbal tea without caffeine, which is also very healthy.  You might also consider coconut water, as you mentioned, which is both healthy and contains electrolytes.  Green tea would also be a good option, as it contains antioxidants and some electrolytes, but less than coconut water.  I hope this helps!
assistant
Very true, coffee does contain carbohydrates and caffeine which are dehydrating.  If you don’t want to include coffee then another good option is to drink some herbal tea.  Many herbal teas also contain significant amounts of electrolytes, for example chamomile tea has 20mg of potassium per serving.  There are many tasty herbal teas to try, for example organic rooibos tea, wild rose, or hibiscus tea.
assistant
I want to avoid eating too much sugar, what is a good alternative to sport drinks to replenish electrolyte?
user
Thank you for asking this question, it is very important to get sufficient electrolyte during exercise.  Here are some healthy alternatives to sport drinks that can help with this:

-Water with added electrolyte packets, also available in most grocery stores.  Recommended brands include Emergen-C and Nuun. 

-Coconut water, traditionally consumed by athletes in the tropics.  Coconut water is very high in potassium and electrolytes, but also contains significant amount of natural sugar which is better to avoid. 

-Green tea with lemon, which is a source of healthy antioxidants.  Green tea also has some electrolyte content, but is less potent than other options. 

-Coffee, which is very healthy but also contains some caffeine and other stimulants which may be undesirable during exercise. 

Hope this helps!
assistant
All great except for coffee since it can dehydrate you due to the significant amount of caffeine.
user