Ok, I'm going to have to step in here and prevent misinformation, because battery safety is an important issue and I think everyone should be in full possession of the facts.
There is NO lithium metal in lithium-ion laptop batteries. In the case of laptop cells (such as the cylindrical 18650 cell you are probably using), and cell phone cells, the lithium chemistry used is lithium cobalt oxide, which does not react with water in the same way that lithium metal does.
In a similar way, the sodium ions in sodium chloride (i.e. table salt) do not explode when you mix salt and water.
Therefore, you CAN use water to help extinguish lithium-ion battery fires, but other types of extinguisher can be more effective, such as sand/salt bucket, ABC dry powder extinguishers, or some class D fire extinguishers. You'd want to avoid water extinguishers if there is a chance of it shorting out other non-burning cells which would exacerbate the problem, but in an emergency, a water hose will work.
We work with lipo batteries on our quadcopters, we have on hand buckets of sand and salt (the salt melts and creates a crust over the battery which helps prevent additional oxygen getting in, and the sand soaks up the heat), and we also have ABC dry powder extinguishers. We're soon investing in a class D extinguisher.
To give you some sources so that you can check this information for yourself (highly recommended), here are some links I quickly dug up via a google search.http://ehs.whoi.edu/ehs/occsafety/Lithi ... deSG10.pdf
(see pages 3 and 13)http://highvoltagehotrods.com/arent-lit ... re-hazard/http://www.apigroupinc.com/news/headlin ... klers.html
It's worth bearing in mind that non-rechargeable lithium cells do contain lithium metal, and you don't use water extinguishers on those types of cell. A lot of people often mistake the two.
- lithium primary cell: contains lithium metal, adding water goes big boom
- lithium rechargeable cell: does not contain lithium metal, adding water is ok
- but still preferably use sand/salt bucket, class ABC dry powder extinguisher, or class D extinguisher