Please don't use water on unfinished wood. It can take days to thoroughly evaporate and be sealed in by whatever you put on over it. That can soften the wood over time. True lemon oil is acidic and not good either. Most inexpensive "lemon oil" is just mineral oil with lemon scent.
I use naphtha (lighter fluid) with an old bath cloth to clean, let it evaporate for 30 minutes and then buff in a small amount of mineral oil. Both are inexpensive and a bottle will last for years. This is what I've used since my dad showed me in 1963. Use a wooden toothpick to get the stuff by the frets.
98% of the commercial fret board treatments are based on mineral oil with some other "magic" ingredients added that may or may not do anything.
If you want to clean and polish the frets, I recommend making something to guard the fret board from scratches. I use two pieces of thin plastic taped together. If you use 0000 steel wool, moisten a small piece with mineral oil. It helps loosen the gunk, keeps the loose pieces together in the area you're working for easy cleanup and reduces the size of the scratch marks. Also put masking tape over the pickups since they will attract any steel wool fibers that get loose. You can also use a Scotchbright pad but they take longer. The green works pretty well.
mech