Definetely not the same as water. Tea helps keep you hydrated, but adding herbs to water completely changes the water. There are many herbs that have a diuretic effect. Don't forget that herbs are actual used for medicinal purposes so over doing any herbal tea that you don't need or is contraindicated by your condition (like if you have too much heat and you are drinking too much fennel or ginger herbs) This will definetely affect you. Also, fennel is known for its lubricating and moistening properties so if you seem to have a lot of mucus and fluid buildup in your digestive system, fennel may make this worse.