Understanding water and sewer
Water is the amount of water coming into your house.  Sewer is (usually) the portion of it that you use inside the house and that goes out through your drains, toilets, etc.  See #2 below.  Sewer charges may also include a portion for storm water if your downspouts feed into a municipal sewer system.
During the summer, it's expected that some of the water will be used for watering your yard, so your sewer usage will be less than your water usage.  During winter, the two should be very similar.
In general, water in bathroom fixtures should be safe to drink, boiled or not; there's only one water main coming to your house, after all.  You may have additional filters on the water lines going to the kitchen faucets, which would make that water taste better (by removing chlorine, say).