I’m aware of the last days vision concerning the destroyer on the waters, however I was wondering why specifically you are not supposed to go in water on Sundays.
As you’re aware, the Lord gave a revelation explaining W.W. Phelps’ vision of the destroyer riding on the Missouri River.
Behold, I, the Lord, in the beginning blessed the waters; but in the last days, by the mouth of my servant John, I cursed the waters.
Wherefore, the days will come that no flesh shall be safe upon the waters. And it shall be said in days to come that none is able to go up to the land of Zion upon the waters, but he that is upright in heart.
And, as I, the Lord, in the beginning cursed the land, even so in the last days have I blessed it, in its time, for the use of my saints, that they may partake the fatness thereof.
And now I give unto you a commandment that what I say unto one I say unto all, that you shall forewarn your brethren concerning these waters, that they come not in journeying upon them, lest their faith fail and they are caught in snares; I, the Lord, have decreed, and the destroyer rideth upon the face thereof, and I revoke not the decree.
The warning concerning the waters focus specifically on the Missouri River (“these waters”), generally on all water routes to Zion (“the waters”), and even more generally when “the days will come” upon all water routes (“the waters”). It is not clear from these verses that the curse was placed upon all waters, including lakes and ponds (or pools and bathtubs, as some urban myths would include).
Note also that while “the days will come” when “the waters” will not be safe, those “days” are not “all Sabbaths”. Any prohibition on sabbatic water activities relates more closely to the holiness of that day. It is dedicated to the Lord and not to our personal or familial recreation. Thus, swimming and boating are minimized, but bathing is highly encouraged.