No leaks, yet high water bill

[Adity Pore]

We are two people staying at a rental property in Texas for 15 months now. On an average our water consumption is about 3000 gallons a month. Since the last 4 months we have been getting absurd amount of water bills. This month we got a 135$ bill for using 15,000 gallons of water. My roommate was out for 20 out of the 30 days we were billed for. I barely used 60 gallons a day during all this time, and I wasn't even home on 13th and 14th NOV and yet the reading showed 270 gallon water usage. The rightmost column shows the gallon usage of water everyday. I did the dye test for toilet leaks, it came negative. I checked the water meter after turning all taps off and I found no movement, that indicates we don't have leaks. I am completely lost and worried about my next bill. Any ideas as to what could be going on?