The vast vast vast majority of people drink way too little water. I drink a little over a gallon a day in addition to the occasional coffee or soda and still occasionally feel the effects of dehydration. I know people who may only have 2-3 glasses of water in a day and nothing else. It's crazy they're still alive.
We have genes that help regulate the use of water in our system. These genes can turn on and off depending on our environment and the availability of water. If you feel the urge to drink over a gallon of water, more power to you, but most of us really don't need that much water. Also, if your pee is consistently clear, you're probably drinking way more water than your system needs.
You may also need to consume more salt and glucose so your body retains more of the water you're consuming. Due to osmotic pressure, your cells can't actually absorb water without the correct salt and glucose to help act as a transport.
Totally agree. I've heard the simplest "test" is to look at your pee color. It should be very light yellow. If it's clear, you're probably overdoing it.