06 Pontiac Torrent - Low coolant, minor leak?

I recently purchased this used "as is" vehicle from a dealer following the destruction of my last car in an accident. Despite all of the terrible complaints following it, I really had no choice but to take the dive on this car due to finances. It was recently taken into the mechanic to have the driver-side wheel hub assembly replaced and was driven by them with no reported issues. The dealer had flushed the coolant system and re-filled it prior to sale.

Today, I drove into work and the car sat parked for about 4 hours in 30 degree weather. On my lunch, I drove the car to the gas station and filled up on gas. Upon my return, I thought to check under the car to make sure all was well (just a thought, not spurred by any sounds or gauges or anything.) I noticed a small patch on the ground under the passenger side, next to the front passenger tire, where water dropplets had accumulated and were resting. It being freezing out leads me to believe this is coolant, as it had not frozen.

I popped the hood and saw that my coolant level has dropped to about 2-3in below the "cold fill" line on the overflow tank. This drop in level must have occurred over the last few weeks, as the last time I checked was about 3 weeks ago. It has been driven a good 500mi since then.

I hadn't thought to check the coolant as my engine heats up normally with the temp gauge consistently resting between 1/4 and 1/2, both when driving and idling. Only once did the temp gauge rise to 1/2, and that was at idle after about 3.5hrs of straight driving. This has not happened since and the temp gauge has never risen higher. I've witnessed no jumps or anything of the sort - it rises as the car heats up and stays steady at 1/4-1/2 until shut off. So, seems normal.

The vehicle also blows excellent heat and A/C and both can be adjusted to a higher or lower temp, no matter if the vehicle is moving or idling.  

The only odd thing I noticed recently is that I can hear a faint sound akin to splashing water behind the dash upon accelerating. I've read that this may be a sign of air in the coolant, but I don't have the characteristic jumps in temp or anything to indicate an issue.

Do you have any idea why I might be losing coolant? And possibly, where I might be losing coolant from?

Also, if I just continue to keep an eye on the coolant level and top it off when I fill up on gas, will I experience any major issues or cause any serious damage? (finances are tight for the next month until I can get it into a mechanic).

Thanks!