The most likely reason for the taste in my water is algal bloom. This taste should fade away as the weather gets colder and the algae dies off.
In the summer, when there is light from the sun and plenty of warmth, algae can bloom on the surface of lakes, reservoirs, and other water sources. While the bacteria is scrubbed from the water during the water treatment process, the moldy taste the algae imparts to the water can be detected at extremely microscopic levels. Some people are especially sensitive to mildew and musty tastes in food (I noticed this well before my husband did, for instance) and it can affect them more.
Occasionally the water has an earthy, musty or fishy taste and odor. These seasonal phenomena can be caused by the bi-annual turnover of our City reservoirs, or with the presence of varied algal blooms in the reservoirs or rivers. It is important to note this taste and odor poses no health concern but one of aesthetic quality.