Water that goes through your water heater will taste different due to aeration and mineral buildup in the water heater. Are you comparing and using straight "cold" water or are you using hot/warm water mixed with the cold?
Try filling two identical glasses with cold water and do a blind taste test. I think the difference in "taste" is due to the fact that you don't drink warm water from your faucet.
Most kitchen faucets can be used with a garden hose. Look for the correct attachment in the hardware store. I also add a double hose attachment. Hook the hose up to one end, close it off. then use the other open end to get the right temp and then open up the garden hose and fill up your tanks. i use this to do water changes to my pond and my tank. It works great.
