Safest method is to use distilled, deoxygenated water (aka electronic water) to remove most contaminants, followed by 99% isopropyl alcohol or 96% ethyl alcohol to remove the rest and also water.
Don't skimp on water and alcohol, submerge the board and use brush while submerged, to pull and dilute contaminants.
Just never use tap or mineral water. You can use regular distilled water as long as you do it quickly, but unless it is deoxygenated it will be corroding so don't leave it in water for long.
Alcohol is there mostly to dilute water so that it dries out very quickly. Without alcohol water could stay under components for a long time and kill or damage your board.
Alcohols can damage some plastic components, so don't keep it in alcohol fo too long, either.
It is also normal to wash a board in ultrasonic cleaner after any rework or at the end of production process (especially in small scale production).
On the other hand if you own an expensive machine that can be reasonably disassembled (ie. almost anything else than a Mac) and you plan to use it for a long time and you don't have any other insurance against spill, then you might be able to save a lot of money with a very small amount of effort.
My laptop was fully beefed up Lenovo T440s and I live in Poland. In Poland, this laptop represented about 3-4 average monthly salaries. Not much compared to half a day of effort to disassemble, clean and reassemble again.
Half a day assumes you have no idea what you are doing and you are need extra time to figure out what to do, find videos on Internet, figure out why you can't pull a part and what still keeps it in place, etc.
For a person that knows what they are doing this is half an hour of effort.
My tip is to always have IPA, distilled water and tools to disassemble and clean your laptop.