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Computers get hot, and they must be cooled. Your average store-bought PC uses a system of fans to pull heat off major components such as the CPU (central processing unit), graphics processor and hard drives. Then the hot air is blown out the back of the machine. That works just fine for most computers doing most jobs. But it's not always ideal, and it does nothing to impress your friends. The other option for dissipating heat is water cooling, or, really, liquid cooling, in which a combination of distilled water and propylene glycol is piped through the guts of the machine. Installing a liquid-cooling system isn't all that difficult, though it can be intimidating. Who can really benefit from this hot-rod project? Mainly, computer users who like to overclock their PCs and run them hard for gaming applications, video processing, sequencing the DNA of Amazonian tree frogs, and the like. Such people often work their processors into a heated frenzy, forcing the fans to run constantly and noisily.

Since liquid transfers heat more efficiently than air, water-cooled PCs can run significantly cooler. (In tests at Popular Mechanics, our liquid-chilled rig ran at 62.6 degrees Fahrenheit at idle - 27 degrees colder than a similar air-cooled computer.) You'll also be able to remove one or more fans, so your water-cooled system will run more quietly. Koolance, Thermaltake, Zalman and other companies sell a variety of water-cooling kits at prices ranging from $150 to $470. (You also can buy the parts piecemeal, but we suggest using a kit for your first water-cooled setup.) A water-cooling system includes a water block, hoses, pump, reservoir, and an external or internal radiator. Make sure you buy a kit that fits your PC's motherboard. It took us about an hour to hook up a Zalman Reserator 2.

Step 1: Prepping Your PC

Preparing your machine is the hardest part. Before you can hook up your water-cooling kit, you must remove your computer's motherboard. That means opening up the case, and unplugging all cards and cables from the board. Make sure whenever you unplug cards and cables, you pull from the connector, not the wire to keep the two from ripping apart. (Note: Take careful note of the setup, as you'll have to reconnect everything later.)

Step 2: Remove the Heat Sink

Once the motherboard is loose, unclip and remove the heat sink. This will have a fan and is in the center of the chip. Make sure not to rip the chip straight off the motherboard. Use a gentle twist and slide motion because the thermal paste already on the chip makes a tight bond. Then clean the top of the exposed chip with an alcohol wipe and apply thermal paste (a conductive metal- or silicone-based grease that should come with the kit).

Pictured here: The heat sink after it is removed, cleaned and the water block is attached (see step 3).

Step 3: Install the Water Block.

Install the water block using the provided mounting bracket. The mounting bracket will sandwich the mother board with a bracket on the bottom and top connected with two screws. As always, and especially with electronics, don't over-tighten the screws.

Pictured: Hoses attached from your water pump and radiator (see step four) will take away heated liquid from the water block and replace it with cooler liquid.

Step 4: Put Your PC Back Together.

Next, put the motherboard back in the case, and reconnect all cables and cards. Use the supplied clamps to attach the hoses to the water block. If your pump and reservoir are separate components, you must run the hoses from one to the other and then into the radiator. (Our Zalman setup was easy to work with, as all of these elements were combined in a single external unit.)

Pictured: Clamping the hoses to the water block is easy âconnect one hose from the water block to the pump and one from the water block to the radiator.

Step 5: Turn It On.

Now, hook up the pump's power cable to the connector coming from your PC's internal power supply.

Step 6: Check for Leaks.

Finally, fill the reservoir with the distilled water/coolant mixture and prime the system, checking all connections for leaks (glycol inside tubesâgood; glycol outside of tubesâbad). If everything is sealed tight, you're good to go.