On my journey losing weight

Firstly how much water you drink has everything to do with staying hydrated but virtually nothing to do with reducing fat. Just drink when you feel thirsty and keep an eye on your pee to make sure you're drinking enough. Pale straw colour is what you're looking for, any darker than that and you need to drink more, lighter than that and you're over-hydrating which has it's own health complications.

Next, weight on the scale is made up of a whole bunch of stuff besides fat, most of which fluctuates by several pounds. Water, waste in your digestive tract and a bunch of other things all contribute towards that number and all will change pretty dramatically each day. The best you can do is to try and minimise the differences and ride out the fluctuations. This means tracking your weight for 3 to 4 weeks at the very least.

I mean, just looking at the numbers you've posted can illustrate this. That the 'weight' you lost in those 5 days was pretty much all 'other stuff'.

- You said you lost 12.5lbs in 5 days. 12.5lbs equates to 43,750 calories. That means you'd need to create a calorie deficit of 8750cal per day which just isn't possible.
- Lets assume that you have a maintenance calorie burn of 2750cal per day (which is probably close if not a little high). This means that in order to lose at that rate you'd need to burn off an additional 6000 calories through activity and exercise. This is of course assuming that you don't eat or drink anything except water for 5 days.
- Now let's assume that you're not starving yourself and eating 1200 calories per day (a bare minimum of food). Now in order to achieve that rate of loss you need to burn 7200 calories per day. This is roughly the equivalent of jogging in place for 8 hours.

So, tying this all together, your day might look something like:
3am - 7am = 4 hours of jogging on the spot non-stop
7am-8am = 200 cal breakfast
8am-9am = commute to work
9am-1pm = Work
1pm-2pm = 500 cal lunch
2pm-6pm = Work
6pm-7pm = commute home
7pm-8pm = 500 cal dinner
8pm-Midnight = 4 hours of jogging on the spot non-stop
Midnight-3am = 3 hours sleep
Repeat every day.

Now obviously this whole thing is utterly ridiculous and is just to illustrate the point. If you maintained even a super aggressive calorie deficit of 1000cal per day, the most weight (as in body fat) you could lose in 5 days would be about 1.5lbs.