You say you don't have time to exercise? Are there any stairs at work? Don't take the elevator, take the stairs at least once a day. If you don't have the strength to climb up then only climb down.
Park farther from the door at work and walk in. Park at the end of your driveway instead of in the garage and walk in. Park on the street (if it's safe for your car).
Buy cloth bags for your groceries and pack them as full as possible. Carry one in each hand from the street to your door.
Do you have time to sit and watch tv? Turn it to exercise time. Building muscle does not require heavy weights and hundreds of reps. While sitting watching tv, life your lower leg, slowly, to the height of your knee then put it back down slowly. Repeat 20 times then switch legs. IF you are partially reclined while watching tv then lift your leg to the level of your knee then lift your whole leg higher than the other knee, slowly, then put it back on the floor. Again 20 times and switch legs. Get a soup can and tie it into a plastic grocery bag. Make "handles" and if you have an armchair, hang your elbow just off the arm of the chair and holding the bag with your fingers facing upward lift it slowly to the point where the can touches your arm then slowly back down to full extension of your arm. Do 20 and repeat.
Need help with your back and upper arms? Take ten minutes to do "push aways". Stand facing a wall and extend your arms in front of you. Back up until your fingertips barely touch the wall. Now on your knuckels lean into the wall with your arms at shoulder width. Keep your body rigid and lower your face to the wall and back SLOWLY. Do only three or four at first but build up to 10. Remember do it slowly. Rest between switches of limbs.
If your knees will take it do not bend over to pick stuff up from the floor, do a deep knee bend for it.
With a little observation of your day, you can create exercises for yourself out of your daily routine.
Congrats on the watching what you eat and good luck. Changing from "normal" food to "healthy" food will help you maintain the weight you want, too. And the gallon of pure water every day is essential but once you get your body accustomed to taking in that much fluid, you can open it up to your total fluid intake. Just remember that coffee and tea are diuretics. They make you loose water so keep them to a minimum. Avoid carbonated water as much as possible, it causes throat cancer. And remember if you have a craving for something you normally wouldn't have on your diet, go ahead and eat it, in a reasonable proportion. Do not ever deny yourself a comfort food just don't make a habit of it or eat too much at once. IF you have a deep craving for ice cream, a single dip cone is not going to kill you. Especially if you walk to the ice cream store to get it!