Yes, it came from whistles on beer mugs.

Pennsylvania State University

Tom Minsker Odds and Ends

When they needed a refill, they used the whistle to get some service.

Answers.com

Answers.com - Where did the term Wet your whistle come from

'Wet your whistle' is the phrase inspired by this practice.

worldwidewords.org

World Wide Words: Wet one’s whistle

When they needed a refill, they used the whistle to get some service.

World Wide Words: Wet one’s whistle

“Wet your whistle” is the phrase inspired by this practice’.

blog.aurorahistoryboutique.com

History Blog » phrase wet your whistle

One of the most widespread beliefs is that “wet your whistle” started during the middle ages in English pubs where whistles were baked into ceramic mugs.

History Blog » Blog Archive » The Origin of the Phrase…Wet Your Whistle

One of the most widespread beliefs is that “wet your whistle” started during the middle ages in English pubs where whistles were baked into ceramic mugs.

History Blog » Blog Archive » The Origin of the Phrase…Wet Your Whistle

According to this theory, when a patron wanted a refill of their drink they would blow the whistle and a barmaid would fill their drink so “wet your whistle” was inspired by this practice.

History Blog » wet your whistle origin

One of the most widespread beliefs is that “wet your whistle” started during the middle ages in English pubs where whistles were baked into ceramic mugs.

PhysicsForums.com

Trivia - true or false.

"Wet your whistle" is the phrase inspired by this practice.

squidoo.com

Strange Facts You Didn't Know

"Wet your whistle" is the phrase inspired by this practice.

Strange Facts You Didn't Know

When they needed a refill, they used the whistle to get some service.

jmm.aaa.net.au

True or False? | John Mark Ministries

When they needed a refill, they used the whistle to get some service.

richardpettinger.com

Funny but True — richardpettinger.com

When they needed a refill, they used the whistle to get some service.

syncrat.com

Lesser known facts - Syncrat Publishing

When they needed a refill, they used the whistle to get some service.

Lesser known facts - Syncrat Publishing

Many years ago in England, pub frequenters had a whistle baked into the rim or handle of their ceramic cups.

Lesser known facts - Syncrat Publishing

"Wet your whistle," is the phrase inspired by this practice.

superkids.com

SuperKids Humor pages. More Little Known Facts

"Wet your whistle," is the phrase inspired by this practice.

SuperKids Humor pages. More Little Known Facts

When they needed a refill, they used the whistle to get some service.

takeourword.com

Take Our Word For It, page one - Spotlight

Wet your whistle, is the phrase inspired by this practice.

rense.com

SIGHTINGS

"Wet your whistle," is the phrase inspired by this practice.

backroadstouring.co.uk

Meanings and Origins of Traditional English Phrases | Back-Roads ...

Many years ago, pub frequenters had a whistle baked into the rim or handle of their ceramic mugs.

Meanings and Origins of Traditional English Phrases | Back-Roads ...

When they needed a refill, they used the whistle to get some service.

flintstonecostume.com

San Francisco Cable Cars | Flintstone Costume

"Wet your whistle" is the phrase Inspired by this practice.

San Francisco Cable Cars | Flintstone Costume

When they needed a refill, they used the whistle to get some service.

austindailyherald.com

Austin Daily Herald | Can you lick your elbow?

'Wet your whistle' is the phrase inspired by this practice.

Can you lick your elbow? | The Austin Daily Herald

‘Wet your whistle’ is the phrase inspired by this practice.

Yahoo!

Would you be interested to know.? - Yahoo! UK & Ireland Answers

When they needed a refill, they used to blow the whistle to get some service.

waynesthisandthat.com

Source's of Popular Expressions

"Wet your whistle," is the phrase inspired by this practice.

boards.straightdope.com

My moral dilemma [Archive] - Straight Dope Message Board

When they needed a refill, they used the whistle to get some service.

My moral dilemma [Archive] - Straight Dope Message Board

"Wet your whistle" is the phrase inspired by this practice.

nikkipixxbooksigninggavsmom1999.blogspot.com

NIKKI PIXX BOOK SIGNING

'Wet your whistle' is the phrase inspired by this practice.

goodwords.com

Ye Olde English Sayings

When they needed a refill, they used to blow the whistle to get some service.

Ye Olde English Sayings

Many years ago in England, pub frequenters had a whistle baked into the rim or handle of their ceramic cups.

Yahoo Answers

Would you be interested to know.? - Yahoo! Answers

When they needed a refill, they used to blow the whistle to get some service.

Do you sometimes feel like you're 'held over a barrel? - Yahoo ...

When they needed a refill, they used to blow the whistle to get some service.

Have you 'wet your whistle' lately? - Yahoo! Answers

"Wet your whistle" is the phrase inspired by this practice.

Where does the phrase "wet your whistle" come from? - Yahoo! Answers

'Wet your whistle' is the phrase inspired by this practice."

bestoday.com.au

Where Did That Saying Come From?, in Writing, on The Billy Lids

"Wet your whistle" is the phrase inspired by this practice.

Where Did That Saying Come From?, in Writing, on The Billy Lids

When they needed a refill, they used the whistle to get some service.

janebluestein.com

Word Facts

When they needed a refill, they used the whistle to get some service.

Word Facts

“Wet your whistle” is the phrase inspired by this practice.

forwardedfunnies.com

Forwarded Funnies: Interesting "Facts"

'Wet your whistle' is the phrase inspired by this practice.

acrossthepond-storyheart.blogspot.com

Across the Pond: June 2009

When they needed a refill, they used to blow the whistle to get some service.

writers-free-reference.com

Funny Story number 57

"Wet your whistle," is the phrase inspired by this practice.

Funny Story number 57

    When they needed a refill, they used the whistle to get some service.   

kcbx.net

Beer Trivia

"Wet your whistle", is the phrase inspired by this practice.

joke-archives.com

Beer Facts

When they needed a refill, they used the whistle to get some service.

mistupid.com

Stupid Facts

When they needed a refill, they used the whistle to get some service.

Stupid Facts

"Wet your whistle," is the phrase inspired by this practice.

dobhran.com

Where Did That Come From? - Best Inspiration from the Net from ...

"Wet your whistle," is the phrase inspired by this practice.

grose.us

FUN FACTS TO KNOW AND TELL:

When they needed a refill, they used  the whistle to get some service.

FUN FACTS TO KNOW AND TELL:

"Wet your whistle," is the phrase inspired  by this practice.

davidstuff.com

facts

When they needed a refill, they used the whistle to get some service.

facts

"Wet your whistle," is the phrase inspired by this practice.

timstouse.com

The Origin of Everyday Expressions

"Wet your whistle," is the phrase inspired by this practice. 

Some Old Expressions

When they needed a refill, they used the whistle to get some service.

johnpratt.com

Did You Know?

When they needed a refill, they used the whistle to get some service.

Did You Know?

"Wet your whistle," is the phrase inspired by this practice.

ojar.com

Useless facts

When they needed a refill, they used the whistle to get some service.

Useless facts

"Wet your whistle," is the phrase inspired by this practice.

funnyandjokes.com

Funny and Jokes » Blog Archive » Did You Know?

"Wet your whistle" is the phrase inspired by this practice.

goofball.com

Fascinating Facts - Goofball.com

When they needed a refill, they used the whistle to get some service.

Fascinating Facts - Goofball.com

"Wet your whistle" is the phrase inspired by this practice.

suddenlysenior.com

Suddenly Senior. Old Sayings, and Where They Came From

When they needed a refill, they used the whistle to get some service.

Suddenly Senior. Old Sayings, and Where They Came From

"Wet your whistle" is the phrase inspired by this practice.

digalist.com

How much encyclopedical things you didn't know

"Wet your whistle" is the phrase inspired by this practice.

surfwiz.com

Amazing Facts and other Funny Ideas

When they needed a refill, they used the whistle to get some service.

jokersrevenge.com

Where Did That Phrase Come From?

"Wet your whistle," is the phrase inspired by this practice.

interestingfactshere.blogspot.com

INTERESTING FACTS: Interesting Facts In the past...

"Wet your whistle" is the phrase inspired by this practice.

datehookup.com

Fun Facts...

'Wet your whistle' is the phrase inspired by this practice.

Fun Facts...

When they needed a refill, they used the whistle to get some service.

coopsjokes.com

Coop's Lists Popular Sayings And Where They Came From...

When they needed a refill, they used the whistle to get some service.

Coop's Lists Popular Sayings And Where They Came From...

"Wet Your Whistle" is the phrase inspired by this practice.

jokes2go.com

Historical Tidbits -- Jokes2Go.com Funny Lists

When they needed a refill, they used the whistle to get some service.

Historical Tidbits -- Jokes2Go.com Funny Lists

"Wet your whistle," is the phrase inspired by this practice.

How can you live without knowing these things? -- Jokes2Go.com Funny Lists

When they needed a refill, they used the whistle to get some service.

websitement-tm.com

Some Weird Facts

When they needed a refill, they used the whistle to get some service.

angelfire.com

Absurd Facts

"Wet your whistle," is the phrase inspired by this practice.

Absurd Facts

When they needed a refill, they used the whistle to get some service.

44 WEIRD FACTS THAT YOU PROBABLY DIDN'T KNOW!

When they needed a refill, they used the whistle to get some service.

weird-websites.info

strange facts odd thoughts silly things that happened for real

'Wet your whistle' is the phrase inspired by this practice.

baconbabble.com

A Momentary Cure For Boredom

“Wet your whistle,” is the phrase inspired by this practice.

myspace

Lucky Lu | Free Music, Tour Dates, Photos, Videos

When they needed a refill, they used to blow the whistle to get some service.

majorwager.com

Misc. Facts - MajorWager Forums

"Wet your whistle," is the phrase inspired by this practice.

youtube.com

YouTube - AMAZING PICTURES

"Wet your whistle" is the phrase inspired by this practice.

1funny.com

Joke: Crazy Facts

"Wet your whistle" is the phrase inspired by this practice.

tealdragon.net

Beer Trivia

When they needed a refill, they used the whistle to get some service.

Beer Trivia

"Wet your whistle", is the phrase inspired by this practice.

sundrania.com

Beer Facts | Sundrania.com

"Wet your whistle", is the phrase inspired by this practice.

snafu.com

Snafu.com - Sayings

When they needed a refill, they used the whistle to get some service.

faculty.scf.edu

British Arcana

When they needed a refill, they used the whistle to get some service.

British Arcana

"Wet your whistle" is the phrase inspired by this practice.

thebrits.com

Fact! | thebrits.com

‘Wet your whistle’ 
is the phrase inspired by this practice.

Fact! | thebrits.com

When they needed a refill, they used the whistle to get some service.

buffam.com

Random Interesting Stuff

When they needed a refill, they used the whistle to get some service.

beersweetbeer.com

Beer Humor / Jokes - Beer sweet beer - beer humor, favorite beers ...

When they needed a refill, they used the whistle to get some service.

digitalwinners.com

The FINEST English Pub Ever ***]

When they needed a refill, they used the whistle to get some service.

miss-charming.com

Miss Charming's Bar Trivia Page

When they needed a refill, they used the whistle to get some service.

Miss Charming's Bar Trivia Page

Wet your whistle is the phrase inspired by this practice.

slazyk.com

Slazyk's Musings » Did You Know…

When they needed a refill, they used the whistle to get some service.

Slazyk's Musings » Did You Know…

“Wet your whistle” is the phrase inspired by this practice.

deaddog.com

DeadDog » 2008» September

“Wet your whistle” is the phrase inspired by this practice.

DeadDog » 2008» September

When they needed a refill, they used the whistle to get some service.

antimoon.com

Famous sayings that come from Britain | Antimoon Forum

When they needed a refill, they used to blow the whistle to get some service.

heartlandbrewery.com

Heartland Brewery | New York City Brew Pub

'Wet your whistle' is the phrase inspired by this practice.

beernexus.com

mr. brewski

when they needed a refill, they used the whistle to get some service.

mr. brewski

"Wet your whistle", is the phrase inspired by this practice.

microsquish.com

Origins of Sayings...

When they needed a refill, they used the whistle to get some service.

sofakingdrunk.com

Interesting Beer/Alcohol Facts | Drink Recipes, Mixed Drinks ...

When they needed a refill, they used the whistle to get some service.

Interesting Beer/Alcohol Facts | Drink Recipes, Mixed Drinks ...

“Wet your whistle” is the phrase inspired by this practice.

raesmith.com

Cool Things To Know

When they needed a refill, they used the whistle to get some service.

potters.org

clayart - thread 'whistle mugs'

When they needed a refill, they used the whistle to get some service.

pottery-magic.com

Clay Pottery Craft Projects Water Whistle

When they needed a refill, they used the whistle to get some service.

Clay Pottery Craft Projects Water Whistle

"Wet your whistle" is the phrase inspired by this practice.

word-detective.com

Issue of May 4, 2004

'Wet your whistle' is the phrase inspired by this practice."

justik.net

Justik.net

When they needed a refill, they used the whistle to get some service.

sandovalsignpost.com

Uncle Duffy- Sandoval Signpost

"Wet your whistle" is the phrase inspired by this practice.

Uncle Duffy- Sandoval Signpost

When they needed a refill, they used the whistle to get some service.

boergoats.com

BoerGoats.com Article facts0

"Wet your whistle" is the phrase inspired by this practice.

craigslist.org

best of craigslist: How can you live without knowing these things?

When they needed a refill, they used the whistle to get some service.

clevelandwomen.com

Cleveland Women | Fun Facts | Women

When they needed a refill, they used the whistle to get some service.

hunto.com

Hunto.com - get all your myspace icons here

"Wet your whistle" is the phrase inspired by this practice.

thecryptmag.com

Random Facts but all True

When they needed a refill, they used the whistle to get some service.

gotoquiz.com

Radom Quiz i made up

"Wet your whistle" is the phrase inspired by this practice.

mainstreetbrewery.com

Beer Trivia at Main Street Brewery

"Wet your whistle," is the phrase inspired by this practice.

Beer Trivia at Main Street Brewery

When they needed a refill, they used the whistle to get some service.

lakesuperiorfishing.com

Lake Superior Fishing Charters, Duluth, Minnesota, Salmon, Trout ...

"Wet your whistle," is the phrase inspired by this practice.

keylimeshop.com

Food Trivia

When they needed a refill, they used the whistle to get some service.

holleymountainairpark.com

Online Fun & Games, Holley Mountain Airpark, "A World Above."

When they needed a refill, they used the whistle to get some service.

toottoot.com

TootToot.com - Yet More Interesting Stuff!

When they needed a refill, they used the whistle to get some service.

welcome2britain.com

London tourist board information. Tourist trivia, facts and ...

When they needed a refill, they used the whistle to get some service.

Goodward Races Tour. Special events in London and Britain

When they needed a refill, they used the whistle to get some service.

sudsandsycles.com

Phrase Origins on suds-and-sycles.com

When they needed a refill, they used the whistle to get some service.

xgboy.com

credssept99.html PPPPPP

When they needed a refill, they used the whistle to get some service.

eduqna.com

Where does the phrase "wet your whistle" come from?

'Wet your whistle' is the phrase inspired by this practice."

soaringwiththeeagles.com

Old Sayings and Their Origins

When they needed a refill, they used to blow the whistle to get some service.

forums.crosswalk.com

RE: Phrases you just don't get

When they needed a refill, they used to blow the whistle to get some service.

dancody.org

Dan Cody – "Left on the Lake" » Medieval Celebration Sayings

When they needed a refill, they used to blow the whistle to get some service.

Dan Cody – "Left on the Lake" » 2005 » January

When they needed a refill, they used to blow the whistle to get some service.

seniorsnetwork.co.uk

Seniors Network - Humour pages

When they needed a refill, they used to blow the whistle to get some service.

forums.singingnews.com

RE: Phrases you just don't get

When they needed a refill, they used to blow the whistle to get some service.

randpersonnel.co.za

Top Applicants Interviewed

When they needed a refill, they used to blow the whistle to get some service.

thc-ministry.org

Old Time sayings - The Hawai'i Cannabis (THC) Ministry : Forum

When they needed a refill, they used to blow the whistle to get some service.

smithchat.com

Sayings & their Meanings - Page 2

When they needed a refill, they used to blow the whistle to get some service.

dailysalty.blogspot.com

The Daily Salty: January 25, 2009

When they needed a refill, they used to blow the whistle to get some service.

geoffdavies.co.uk

Geoff Davies

When they needed a refill, they used to blow the whistle to get some service.

karenzo.blogspot.com

karenzo.blogspot.com

When they needed a refill, they used to blow the whistle to get some service.

stuyoung.pwp.blueyonder.co.uk

The Origin of Phrases by S

When they needed a refill, they used to blow the whistle to get some service.

worldthroughthelens.com

The origins of old England phrases, sayings and words

When they needed a refill, they used the whistle to get some service.

The origins of old England phrases, sayings and words

"Wet your whistle" is the phrase inspired by this practice.

bellatryx.blogs.ie

Side Effects (of living and being me) :: Information

When they needed a refill, they used to blow the whistle to get some service.

slashfood.com

Did You Know 11? - Slashfood

When they needed a refill, they used the whistle to get some service.

Did You Know 11? - Slashfood

'Wet your whistle' is the phrase inspired by this practice."

merchantserviceaz.com

Fun Stuff You Didn’t Know!

‘Wet your whistle’ is the phrase inspired by this practice.

bordeaux-undiscovered.blogspot.com

Bordeaux-Undiscovered: Wine Trivia - As Drunk as a Skunk

"Wet your whistle", is the phrase inspired by this practice.

redrag.org

Beer Trivia

"Wet your whistle", is the phrase inspired by this practice.

No, the word "whistle" was a slang word for throat.

jefflewis.net

Factoids Debunked & Verified, Part II on jefflewis.net

False- Whistle used to be a slang term for your throat, so the expression simply means to get your throat wet.

phrases.org.uk

Whet your appetite

This is complete tosh.

blog.aurorahistoryboutique.com

History Blog » Blog Archive » The Origin of the Phrase…Wet Your Whistle

That sounds like a plausible story but it does not seem to be accurate since no examples of the mugs have survived and any pottery sold as such are fakes or souvenirs that attempt to validate that origin of the saying.

History Blog » Blog Archive » The Origin of the Phrase…Wet Your Whistle

Another thought is that it was simply a catchy reference to the mouth and throat.

History Blog » Blog Archive » The Origin of the Phrase…Wet Your Whistle

Indeed it is mentioned in Chaucer’s Canterbury Tales which was published at the end of the 14th century.

History Blog » Blog Archive » The Origin of the Phrase…Wet Your Whistle

The term never actually referred to a whistle but to the fact that it is hard to whistle with a dry mouth and also “wet your whistle” made it sound like taking a drink was necessary.

History Blog » Blog Archive » The Origin of the Phrase…Wet Your Whistle

This sounds like a much more likely origin of the phrase even if it is less imaginative than the mugs with whistles baked into them.

History Blog » English language history

Indeed it is mentioned in Chaucer’s Canterbury Tales which was published at the end of the 14th century.

History Blog » Canterbury Tales

Indeed it is mentioned in Chaucer’s Canterbury Tales which was published at the end of the 14th century.

History Blog » wet your whistle origin

That sounds like a plausible story but it does not seem to be accurate since no examples of the mugs have survived and any pottery sold as such are fakes or souvenirs that attempt to validate that origin of the saying.

Yahoo Answers

What does the phrase, "wet your whistle" mean? - Yahoo! Answers

So, to wet your whistle is simply "to wet your throat".

takeourword.com

Take Our Word For It, page one - Spotlight

A written description of one, perhaps?

Take Our Word For It, page one - Spotlight

A picture of one?

Take Our Word For It, page one - Spotlight

Has anyone ever seen one of these mugs?

Take Our Word For It, page one - Spotlight

Of course not, they never existed.

Take Our Word For It, page one - Spotlight

Since the middle ages, whistle has been used as a slang term for the throat.

Take Our Word For It, page one - Spotlight

So, to wet your whistle is simply "to wet your throat".