I don;t drink that much during the day. I drink probably about 2-3 cups of milk and the rest of the day i drink water. I end up drinking about 2 bottles of water a day.
I believe it is water weight. Your are not drinking enough water during the day, especially if you are working out. Your body is trying to hang on to the water it needs by storing it.
There are many reasons someone can gain weight during a given time period. In a lot of cases it has to do with temporary changes to your normal routine. Example: You usually are up and moving around a lot in your normal daily routine (work, school, etc.). However for the last 3 days you've been in an all day meeting/lecture just sitting. Thus while you would normally walk about 10,000 steps (about 5 miles) in a day, you're now walking only 3,000 steps (about 1.5 miles). The treadmill workout you listed would give you another 1.75 to 2.0 miles each day so you would have had a net decrease in walking of about a mile each day.
Hopefully you aren't weighing yourself every day and expecting to see results. It is quite common to have weight movement day to day as well as during the course of a given day. Weighing yourself once a week under the same conditions is more than enough! Remember the weight you're trying to get rid of wasn't added over night so it won't disappear over night either.
Using your new treadmill on a regular basis (at least 3-4 times a week) will help in the long run because it will change your metabolism and in the long term help you keep from easily gaining the weight back that you've lost.
Cheers From Texas....