DONOr/ACCEptor ADD have some issues, and do not work properly in older versions of CHARMM. It is really very easy to regenerate the PSF so I strongly recommend that route; if your water segment is the last one all it takes is:
read rtf card name ... ! the new RTF w/ DONO, ACCE for TIP3
read param card name ..
read psf card name old.psf
delet atom sele segid wat
read seque tip3 345
gene wat noangle nodihe
write psf card name new.psf
* PSF for ... with DONO/ACCE for TIP3
*

If water residue numbering in the original PSF was not sequential one may change it to sequential with the JOIN command (struct.doc).


Lennart Nilsson
Karolinska Institutet
Stockholm, Sweden