usually only the 95% is legal in most countries (without a licence): too much diversion into illicit ie tax free alcoholic drinks.
peronally i wouldn't drink it unless i knew it was distilled from cane sugar ferment, as most other processes (from coal, etc) for making it leave a nasty benzene residue. which is not a problem for cleaning boards. the residue you seee in 95% is from more than just water: pure water of course leaves no residue when it evaportes. try the difference between tap water and distilled or RO water if you don't believe me.
Isopropyl alcohol would be better at removing oily stains from circuit boards than the ethyl alcohol, BTW. it's less polar, but it does evaporate more slowly as a drawback...
unless you keep your 99% alcohol on a molecular sieve or other drying agent, it very quickly becomes 90% alcohol by absorbing water vapour from the air. try anhydrous calcium carbonate pellets for a cheaper solution. you need to bake them to drive off water that they have abosrbed first, then cool, then pour about 50-100g into 1 L of alcohol. can strain them out and recharge by baking again in a few months.