Neptune’s Revenge?
Well, if it isn’t Flow Job. How’s it trickling, Wah-wah? Babbled any brooks lately, Splashy? Your mom’s a douche, your dad’s an enema, your brother’s a squirt, and your sister pumps Poland Spring.
Get lost, Skywank.
Spigotto (especially to mock bottled water)
Pipe soup
I love this one and am going to start using it.
That rain, it’s God having a slash.
W.C. Fields: “Never touch the stuff. Fish fuck in it.”
I’ll tell my brother he’s in cultured company 
(see Perjorative names for water - #16 by griffin1977 )
Turd Bath
Dunky
Soak’ums
Splatterpuss
Dousebucket
Judi Drench
Flush Limbaugh
Slosho
Weeping Willy
Seeping Sally
Floodzilla
Dr. Leaky
Gushers
Her Moistness
PlungeBob
Spigot splooge
Creeksqueak
Sopworth
Dropsy
Swigglet
Gurgley
Dewlap
Eisenshower
Lake Titicaca
Glug-glug
Dewpoint
Septic Sally
Dr. Trickle
Mr. Hydro
Rinse Cycle
Flats Seltzer
Birdbath
Quenchy
Sudsy O’Dishpan
Boatfloat
Spitzer Swallows
Whalespout
Lady Dilute
Pissy Riot