"needed" for what, exactly? I was going for a mnemonic to assist in recall. It could be one sip of water and also be effective, although repetition is important.

Are you talking about filling your bladder so it wakes you up to urinate? If so - that's *hugely* variable person-to-person. And is also going to depend upon your metabolism, prostrate activity, and similar factors. So it will change even for a single person night to night.

Also, no guarantee your bladder is going to wake you during REM either.