so like diving a bit? that's actually the only way i know how to swim lol. i don't know how to swim at all
Sure. One could just stand upright in the water. There could be a short period of distress between losing consciousness as you begin to drown but it would likely be incredibly subtle. I think the ideal circumstance would have your head and body supported by something (e.g., a ladder, log, whatever) until you reach the point you can no longer support your own body being upright.
I often imagine a large bathtub as well with a sharp incline where one would naturally slip into the water along the incline as they lost consciousness.
One would need to get a bit creative to avoid any distress during the absorption period where one is in the process of/on the brink of losing consciousness. I suspect the distress would be small or insignificant and others who have survived report it to be quite peaceful.
Hope this helps
As always I encourage people to do a lot of psychospiritual preparation for dying, including support from loved ones
where possible (I know this can seem an impossible task for many given suicide stigma/prohibition, but if it's possible it is worth its weight in gold) and of course seriously deliberate options for both living and dying preferable over a number of months at the least (perhaps even a year or two).
But, it is never my place to tell people what to do beyond encouraging reflexive introspection & consideration :)