usually best way is small amounts at a time. if you ever burned a single sheet of paper. nothing is left. if you burn whole ream (500sheets) of paper some survive unless you break up the wad.
same goes for water. need to break it up.
This is evidently true. To me it all depends on you and how much importance you attach to the said documents that needs to be totally erased. The easiest and fastest ways doesn't seem safe and as such, I'll recommend what I do and it's been effective for me though, it's a very slow means as, you can't do that all at once to a ream of papers and that is, you've got to shred it and not just the regular lateral pattern but both horizontally as well to form a check or net patterns and then, you dump it randomly at different locations based on how your movement is scheduled for the day. It would take more than being a genius to put the pieces together.
a cross cut/confetti shredders are useless. they have already shown that someone can put the confetti. print side down onto a scanner and use a computer program to put them back together..
its like a jigsaw puzzle solver that takes seconds for computer graphics programs these days
bleaching alone doesnt work as although it can fade the inks. it does leave traces and again a computer program can just use spectral analysis(measuring the minor changes of colour tones) to then regenerate the words.
turning the paper into sludge/mache. or burning it to dust is the only true way.