okay, let me get this straight...
1) Belldandy uses mirrors

 Yep.

2) Skuld uses water

 HOT water, not just water. In the manga she
materializes first in Urd's bathtub (hot water) but when she
see's Urd she runs away (through the bathwater again) into
Keiichi's cup of tea,

As has been pointed out in my previous posts, Skuld's been seen teleporting 
through cold water as well.  A contradiction there that's caught me by suprise. 
For example, in Aa! Megami-sensei! #4, I had Skuld heat up a beaker of water 
before teleporting through that.  It wasn't until later that I got the manga 
volume that had the ocean scene in it.

3) Urd uses televisions.

 Hmmm.. This is where it gets strange, actually I
believe she's powerful enough to use any medium. Again, in
the manga, the first time she appeared through the TV, but
when Skuld entered the series Urd started chasing her, Skuld
tried to escape going through Keiichi's cup again but Urd
followed her *through* the cup (which ellicited the
exclamation after the transport "Hey! What's the big idea
with moving through a teacup anyway Skuld?!?"  which
degenerated into one of their traditional fights).

I suspect it's more like a "tunnel" effect where Skuld's teleportation left a 
sort of trail for Urd to follow.  I have the first 12 volumes of the manga (the 
13th is available in a few places in the US, from what I understand), and I've 
never seen Urd use any means of teleportation other than video screens and the 
Skuld incident mentioned above.

is that right?

 More or less. :9

-RangerElf

Peter L. Ward          falcon@best.com          Kyusaku on IRC #Anime!
Caretaker of the Urd Shrine (http://www.best.com/~falcon/urdhome.htm)

"Okay, *here's* an idea...I've heard the best cure for memory loss
 is...SHOCK TREATMENT!!" - Urd