Science: Water temp over time

Every few weeks or so we make a trip to the water store to fill up our 3 gallon water container all while trying to avoid their delicious Santa Cruz ice cream. Upon arriving home, the container gets put into the refrigerator. At which point I started to wonder about the effect of the ambient temperature and how long it takes the water to reach equilibrium.

My first attempt went pretty well. Here is the hardware I used, most of what I had available except for the waterproof temp sensor and the food grade heat shrink.

DS18B20 - Waterproof temp sensor - Adafruit
Food-grade heat shrink tubing - Adafruit
Arduino Leonardo
Arduino Ethernet Shield (for SD Card)
Cardboard box
SHT1x Temp\Humidity Sensor
Tenergy 7.4v 5200mAh LiPo Battery - All-Battery

I started at 8:47pm and the battery lasted until about 6:15am. I didn't get a chance to fully charge the battery but I received a good amount of data. The sketch took a reading and logged it to the SD Card every ten seconds.

What is interesting about the data is the humidity seems to have a direct relationship to the ambient temp of the refrigerator.

Next time, I want to log less often and hopefully get a full data set where the water temp reaches closer\matches ambient. Also I need to track when the door opens either manually or with a sensor (a light sensor would work here).

Overall it was a fun experiment and it is definitely something I want to investigate further and possibly make it a permanent setup - as far as monitoring the refrigerator, if I can get a wireless link. This could be extended further with notifications if the temp rises above a threshold.