read file to_pdb.pdb atoms pdb
key protein select .n segm name WAT* ION end
key solvent sele .not protein end 

calculate pair each_closest select .not. protein end \
    select protein end range 0. 1000.
! only opens the file
write over file to_pdb_2.pdb sele .not all end coor pdb
set vari iseg = 0
<write_by_pair ires nresid iseg to_pdb_2.pdb
quit