My v6 explorer has developed a puzzling issue for me.

Last friday while on a 100 mile trip, the temp started climbing at red lights and then would drop once moving again. When I got home I checked the coolant to find I had none left in the resivior.

I still have to drive this about 30mi round trip each day so I have been adding water to the resivior prior to my journey each morning. When I check the resivior at the end of my 15mi commute, it's empty again and I have to refill to get back home.

Last night I filled the resivior up before going to bed only to find it all gone this morning an I had to refill it.

So far it is running just like normal without temp changes since that 100 mi trip. I checked the oil and it doesn't seem out of the ordinary. It's 2k miles old but still has a nice brown color to it, not black. Could this be water in the oil making it look like it's brown?

No smoking out of the exhaust pipe. The puzzling thing to me is there are no puddles under the vehicle, nor can I find anywhere that appears to be a leak.

Does anyone have any idea where this water is going and where it went to begin with? Should I keep driving it as is by adding water every time I go somewhere?

I am planning to take this to get worked on but I can't do it until this weekend when I am off work.