I'm in hot water.

December 28, 2005 7:52 AM

Why does hot water come out of a kitchen faucet with a milky and cloudy appearance while cold water comes out (same faucet) clear as a bell? No discernable difference in taste.
posted by punkfloyd to Grab Bag (22 answers total)

Just a wild guess here, but I'd say there's something fishy going on in your hot water heater...
posted by jcruden at 7:57 AM on December 28, 2005

I think it's the air bubbles that form in the heated water? After all, doesn't it clear up after it's in the glass??
posted by matty at 7:59 AM on December 28, 2005

Dissolved bubbles.

Pour hot water into a (thick) clear glass. Stare intently. Watch bubbles drift upwards and the water slowly clear-ify.
posted by By The Grace of God at 7:59 AM on December 28, 2005

Some quick Googling and I get this:

However, a water tank is a sealed environment, so as the water is heated, pressure builds up in the tank, artificially holding these gases in their dissolved state. When water is drawn from a faucet and released from the tank, the pressure is lowered, causing these gasses to vaporize and form tiny bubbles in the water, giving it a milky appearance.

Skimming some wikipedia articles leads me to believe it can also happen more readily on faucets that mix the hot and cold at the tap.
posted by mikeh at 8:01 AM on December 28, 2005

Don't drink hot water from the tap. It will pick up plumbing solder and pipe metal, as well as water impurities that have precipitated in the pipes. Although what you are seeing is probably dissolved air.
posted by StickyCarpet at 8:02 AM on December 28, 2005

I second Sticky Carpet's advice. Hot tap water should never be consumed.

Additionally, most of the lead in tap water comes from contact with the faucet. It is good practice to let the water run for 10 seconds or so, to flush out and dilute any dissolved lead that may be in the first "plug" of tap water.

And it's bubbles, in the hot tap water, as everyone else has mentioned.
posted by Danf at 8:10 AM on December 28, 2005

Er, isn't that really only a problem if you have lead pipes, which most people, uh, don't? I don't think brass is harmful for you, and do people even solder pipes anymore? I thought it was mostly just screwed in place with o-rings.
posted by delmoi at 8:13 AM on December 28, 2005

It's aeration in the water, nothing harmful at all, just air.
posted by essexjan at 8:32 AM on December 28, 2005

Lead wasn't banned in pipes until 1986 in the US, delmoi. Unless your pipes are less than 20 years old, there's a chance there's lead somewhere along the line.
posted by bcwinters at 8:37 AM on December 28, 2005

I did a small chemistry study in college, testing for lead and impurities using hot water from faucets with lead pipes. Never found any lead or any metals, even in the parts per billion range, so I don't think StickyCarpet or Danf's advice is right. But maybe they have some data I don't know about--and my experiment surely wasn't confirmatory.
posted by gramcracker at 8:39 AM on December 28, 2005

It is good practice to let the water run for 10 seconds or so

Or, from another perspective, it's a waste of water.
posted by Kirth Gerson at 8:47 AM on December 28, 2005

I have had my hot and cold water tested and hot did indeed have impurities. This is a function of is how old your plumbing is, the more recently it was installed the worse the solder issue is. If its been worked on real recently there is probably flux in the lines as well (a solder catalyst paste.)

The quality of craftsmanship is an issue too, a pro leaves very little solder in the line, a handyman can leave a lot.

And gramcracker, you are telling me you drink water from lead pipes? Some say the attendant mental ailments that can cause led to the fall of the Roman Empire.
posted by StickyCarpet at 8:47 AM on December 28, 2005

It is good practice to let the water run for 10 seconds or so

Or, from another perspective, it's a waste of water.

On this issue I recall that during a water shortage in NYC, Mayor Koch did TV spots telling people that, despite the shortage, everyone should make sure to let the water run for 30 seconds before drinking.
posted by StickyCarpet at 8:50 AM on December 28, 2005

Obviously none of you live in DC.

A few years ago, it came out that a huge portion of the city's water pipes were lead. Had nothing to do with the plumbing in your own building -- these were the city-owned lines.

So yes, there are still plenty of lead pipes around.
posted by occhiblu at 9:02 AM on December 28, 2005

Many new houses have PVC pipes, with almost no solder joints.

I'd be wary of generalizing from the mayor of New York's statement to anywhere else on the planet.
posted by Kirth Gerson at 9:04 AM on December 28, 2005

I'll take a pass on drinking water from PVC pipes.
posted by StickyCarpet at 9:10 AM on December 28, 2005

do people even solder pipes anymore?

Yes. On the plus side, modern solder contains no lead, but in older buildings....

Some say the attendant mental ailments that can cause led to the fall of the Roman Empire.

Others say that's hooey. For a discussion, consider this (among others).
posted by IndigoJones at 9:11 AM on December 28, 2005

Tangentfilter: DC-area tap water analysis
posted by grateful at 9:58 AM on December 28, 2005

When I lived in San Antonio, really hot water flowing out of the tap was quite milky. This was because there was an awful lot of limestone in it.

See, the tap water in San Antonio comes from something they call the aquifer; essentially, a big batch of underground water that resides betwixt two massive sheets of limestone. On the up side, the limestone filters out all other impurities and the water is extremely low in pollutants. On the down side, water with lots of limestone in it tastes awful.
posted by Clay201 at 12:07 PM on December 28, 2005

Lead or not, hot water is not considered clean water. Your hot water tank is prone to a build up of all fashion of pollutants and what not. It's probably not the most pressing health issue, but since you have the clean, cold water right there, it's just better not to drink the hot water.
posted by teece at 1:17 PM on December 28, 2005

Water pipes aren't PVC. White Sewer pipes are. (The black ones are ABS)

Water supply pipes are polybutylene, polyethylene, or polypropylene. The materials are chosen specifically to avoid toxins diffusing into the standing water in the pipes.

Hot water comes out of my office's taps cloudy with bubbles, but clears up on the counter. Ice cubes made with this water produce white flakes of scale at the bottom of a glass when they melt, so there is disolved lime in this water. We have hard water here.

Cold water at the office doesn't exhibit the scaling problem.
posted by Crosius at 1:27 PM on December 28, 2005

The molecules are agitated. When they calm down (when you let the water stand for a few minutes), the water clears again.

We had this happen when we got a new central heating system. The old system used a tank in the loft and the hot water was pre-heated. The new system uses a combi-boiler and the water is heated on demand. The water pressure is higher and the water is heated more quickly. Hence the agitation.

There's a word for this -- a correct, scientific type word -- but I can't remember it. Basically, it comes down to my first sentence.
posted by mtonks at 12:48 AM on December 29, 2005