Why is my coolant light blinking???

[AUDIOGUY]

Since it started to get a little cooler, my coolant light blinks intermittently for the first few minutes of running. I then turn the car off and back on and the blinking is gone. I have coolant and the car hovers at 180 temp reading. I am wondering if the cap is bad... I have seen a little moisture on the inside of the deck lid from time to time.

If I need to top off the coolant, is there a suitable "non-porsche" I can buy locally or should I go with distilled water?

Any ideas?
Car runs fine by the way.