Noticed few drops of antifreeze (2" diameter) on driveway under 98 Accord which probably occurred over last week. Resevoir level is down to min line. Added 10 oz of water to resv min/max line. Cause?

It's very difficult to say where the drops are coming from just from here looking at this, and not the car. For one thing, always use distilled water if at all possible, in a roadside situation where you have to add tap is better than nothing. If the coolant has not been changed in several years, it's probably time to do so, a 50/50 mix of un-diluted coolant or pre-mixed.

Also Make sure you look on the reservoir for the cold level fill marks, don't over-fill cold or it will spit it out. And a 50/50 will protect it well below zero °F. The only vehicles that need a 60/40 or 70/30 are if wherever you are gets to like 20 below.. ever.

If I had paid attention I would have noticed you did look at the marks. And just to add, a 1998 model car, any car, with no drops of any kind is the anomaly, not the norm.