What is the best sealant to use on a wooden counter that is not harmfu

Are you talking about a butcher block counter? you use food-grade mineral oil.

You can find "butcher block oil" at Lowe's... specially made for surfaces where food will be prepared

do you want it to be impervious to stains? That makes your probelm more difficult, as the only real solution is to polyurethane it. however, I use mineral oil on mine and have for decades. it will stain, but you can scrub it and resand it if that is an issue. Just pour it on the wood and spread it around. let it sink in for a while, and then wipe off the excess. scrub thoroughly before hand though.

you may also use polyurethane, most bars use that.

Polycrylic by Minwax. Blue label on can. Takes 5 coats then waterproof.

Depends on what kind of wood. Is it a wood top that had already been sealed? Or is a butcher block top? Wood tops can be sealed with polyurethane. Keep the area well ventilated. But butcher blocks or wood surfaces that are used for cutting on are just sealed with oil. Coconut oil, linseed oil, mineral oil... there are several choices.

Is there a sink installed in it? Sounds like you could just use oil.

I would coat it with a few coats of pour on epoxy/resin. It will keep the wood from being marred or stained or warped.

I would just use oil then!

I have wood butcher block counters and use bees wax for wood on mine. You have to use a product that is food grade, as you know.