Oil soaked lettuce leaf found on counter – food safety issue

This is a very broad question. My recommendation is to look up your specific product at the US FDA Food Safety page.

Some of the topics treated are:

Product-Specific Information

Acidified and Low-Acid Canned Foods

Bottled Water & Carbonated Soft Drinks

Cheese Safety

Egg Safety

Fruits, Vegetables & Juices

Infant Formula

Medical Foods

Milk Safety

Seafood

Food Allergens

Consumer Information

Food Allergens Labeling

Foodborne Illness

Consumer Information

Foodborne Illness, Foodborne Pathogens & Natural Toxins

Interagency Coordination

Food Contaminants & Adulteration

Chemical Contaminants

Metals

Natural Toxins

Pesticides

What you're trying to kill in both cases is different.

When you're cooking meat, you're mostly trying to kill the organisms which infect meat: listeria, salmonella, trichinosis, roundworm, etc. All of these organisms die at 165F after a few minutes. Further, presumably you're buying government-inspected meat which has very few, if any, of these organisms to begin with. Were you, for some reason, eating "risky" meat, it would be a better idea to cook it to a higher temperature (or not eat it in the first place).

On the other hand, when you're purifying water, you're trying to kill not only organisms like e.coli and cholera (which die quickly at relatively low temperatures), but organisms like giardia and cryptosporidium, which can survive much higher temperatures for brief periods. While it's possible to kill them at 165F, you would need to hold the water at that temperature for more than 30 minutes. It's far easier to heat the water up to 190F or higher, which will kill organisms in less than a minute.