Q: Car has been shutting down for 9 months

For about nine months, my car has been shutting off. First, I replaced a couple of ignition coils and it ran fine until about 2 weeks ago. There has been some sputtering, but it is hard to detect it. I had thought I might have imagined it because it happened so quickly. One day, I had to go back inside the house, so I left it idling and it turned off. I started it and started driving. I got ½ way from my destination and it shut off. I hit on the ignition coils and then it would start before quitting again. Some other details: somewhere there is a leak or evaporation, the radiator was low. Daily, I have to add water. The day after filling it up with water, it broke down, but drove home fine. An additional time (to the 2 coils mentioned above) I replaced 2 ignition coils (that’s twice in 9 months) and everything has been fine since. But it goes through the whole problem again if I don’t put water in the radiator, plus problems with the ignition coils. I also can’t find the leak. Please tell me what I’m doing right and what I’m doing wrong and what is your advice. Thank you.