I'm pretty sure
that Rexair started making the electric hoses for Wet Pick up starting with the Blue production of Rainbows. The Aquamate 3 was introduced around that time I believe (not 100%). My gold 2 speed's original electric hose was not made for wet pick up, however, I bought a new hose a LONG time ago from Goodvac I think, that was the updated hose for wet pick up, so I could buy an Aquamate 3 to use with my rainbow. All the rainbows made since then used the electric hose suitable for wet pick up because they NOW offered the Aquamate 3 (which requires the electric hose)...in other words, any model from the Blue ON should be able to be used for wet pick up (UNLESS someone has replaced the hose it came with with an OLDER rainbow electric hose)
Geez, I hope I got that right!