I have found that the taste of the fresh water does change after having the sugar water in my mouth. My taste buds adapted to the sugar water. As the sugar water stayed in my mouth longer the water started to taste less sugary. The fresh water tasted more like chlorine and dull than it usually does. Since my taste buds had adapted to the sugar in the water, when I put the regular tap water into my mouth my taste buds were kind of shocked because they had been adapting to the sugar water and they got interrupted with regular tap water.
Receptors sensed the taste of something in my mouth. My brain told me that it was a familiar taste and that taste was sugar. The sense that was affect was gustation. There only has to be one gram of sugar in one million grams of water for us to taste it.
It would be a very slight taste and some may not even taste it. If you were to do this and taste the water immediately then the taste would not be as strong as if you let the water sit for a couple of hours. The longer you let something sit the more it mixes together. If you were to heat the water it would speed up the process and you would be able to taste the sugar stronger sooner. The longer you let it set in your mouth the more your taste buds get used to it and the less likely you are to taste it. Your body can adapt to almost any taste.
If you do this experiment, it helps explain why when you come into a warm house in the dead of winter you feel hot. Your body adapts...