Waterblocks are pretty much the heatsink of water cooling. They go onto your chip, take the heat, and put it into the water which then gets cooled by your radiator. You can get waterblocks for pretty much anything. CPUs, GPUs, RAM, HDDs, and motherboard chipsets. Though, as I said, GPU and CPU cooling is usually the only thing you'll be looking at doing unless you're an enthusiast. Picking a waterblock is pretty easy. There's not much to it, besides one thing - Nickel plated VS not nickel plated. If you're on a tight budget, get a non nickel plated waterblock. If you have some money to spend, get a nickel plated waterblock. The difference is that having nickel plating makes your waterblock much more resistant to corrosion which means it will last a lot longer and keep your loop cleaner.

Contrary to popular belief, it doesn't matter if the top of the waterblock is clear plastic or stainless steel or whatever. It's all just looks. Get what you think looks best and has a decent number of positive reviews.

The reservoir is the part of your loop which keeps your tubes bubble-free. This is also where you will be pouring your coolant in.
There are three types of reservoirs. The most common type is called a bay reservoir. This reservoir will fit into one or more of your 5.25" bays usually. Some cases don't have space for bay reservoirs, which means you'd have to look at a different kind of reservoir, like an internal reservoir. These are usually cylindrical in shape and can be mounted anywhere in your case where you have room. Lasly, you can get an external reservoir which, obviously, is mounted outside your case or on a stand.

Bay res example-
[ Register or Signin to view external links. ]

Internal res example-
[ Register or Signin to view external links. ]

The size of a reservoir will not noticeably affect your overclocking performance. The only real advantage of having a bigger reservoir is that bleeding your loop will be a lot easier and a lot faster.

The radiator is the part of your loop that takes in hot water and puts out fresh cool water. It works by squeezing the water through little pipes with little heatsink-like fins which are cooled by fans. Radiators are made to be mounted onto the fan ports on your case, however, you can buy an external stand and have it outside your PC if you like. There are various sizes of radiators. Obviously, a bigger radiator means more fins which means cooler water, so always try to get the biggest one your case will allow. The radiator sizes are defined by how many fan slots they take up. Examples would be 4x120mm(480mm) and 2x120mm(240mm). Other times they're just called double(240mm), triple(360mm) or quadruple(480mm). There really aren't any technical specifications you have to look for when choosing a radiator because they're all very similar. Just try to find one with a decent amount of good reviews for durability and other such things.

A radiator looks like this;
[ Register or Signin to view external links. ]

Choosing the right tubing confuses a lot of people but it is really quite simple. I'll try my best to explain it to you now. There are two tube size measurements. Inside Diameter or ID and Outer Diameter or OD. If you are going to use barb fittings, forget about the outer diameter. It doesn't matter at all. If you are going to use compression fittings, you must take into account both the ID and the OD. The fittings section will tell you the difference between barb fittings and compression fittings.

You should do some looking around on google images or youtube to figure out what size you like the looks of better. The size of your tubing barely matters for performance at all. Obviously bigger tubes allow more waterflow which means better temperatures, but the difference isn't worth building a loop which looks ugly to you.

The next thing to consider is the ID or Inner Diameter. This is simple. The larger the Inner Diameter is, the more waterflow you get, but the less you will be able to bend it before it kinks. If you have a smaller ID, there will be less space for waterflow, but you can bend the tube more before it kinks.

There are also two main types of tubing. The most common is just standard PVC tubing. This is usually what you think of when you hear tubing.
If you have some extra money, you may want to consider Tygon tubing. Tygon is actually just a brand, but I felt the need to give it its own separate category because it is laboratory grade high quality stuff. It's a bit more expensive but more kink, corrosion, and aging resistant.

For a normal watercooling setup, you will want to purchase 10-15 feet of tubing to be safe. It's better to have 3 feet of extra tubing than to put your whole loop together to find out you're 3 inches short.

Fittings are just little metal pieces that you use to connect your tubing to your reservoir, waterblock, etc. Each watercooling part requires an input fitting and an output fitting IF it does not have built in fittings. Picking the right ones has everything to do with what tubing you chose. There are two different kinds of fittings- barb fittings, and compression fittings.

Barb fittings;
These are the cheaper option. All you do is push them onto your tubing and they stay on via a barb. Using an additional clamp is optional, however, I highly recommend it. I wouldn't be able to live knowing that my tubes are just held on by a barb like that. If you don't want to spend money on clamps, you can also use zipties.

Compression fittings;
These are a lot more expensive than barb fittings because they're safer and more secure. You put the tubing onto the fitting like a you would with a barb fitting, but there's an extra piece that you screw onto the barb part which secures it firmly in place.

There are also three different finishes you can choose from. Note that these do not affect performance at all. Black is generally the most expensive finish, but it's just paint. If you get black, be careful not to scratch the paint off. Nickel plated is the most popular choice. Lastly, you have black nickel which is shiny like normal nickel plated fittings, but it has a grayish tint.

The coolant is obviously the liquid which you put in your loop. You can just use distilled water if you'd like. However, I recommend purchasing a non-conductive coolant because if it leaks, it won't short out any of your components and end up costing you money. 1 liter will fill most normal-sized liquid cooling loops. If you've got lots of tube going around and/or a huge reservoir, you may have to get a little more.

If you're really worried about the life of your loop, stay away from colored coolants because the dyes can leave residue in your tubing and reservoir. You can clean it out if this happens by running distilled water through your loop, but it could get annoying after a few times. However, don't get disappointed if you were really looking forward to seeing some intense colors. If you put clear coolant in colored tubing, you won't know the difference.
Example;

The coloured tubing looks a little nicer IMHO. Coloured coolant is usually opaque, whereas coloured tubing is usually transparent.

Picking your coolant is probably the easiest part. As long as it's non-conductive and not an extremely notorious brand, you can get pretty much whatever you want.

The way your loops works, is as follows;

>->Reservoir>->Pump>->v
^<-<Radiator<-<Block<-<

One thing that I can't illustrate in this diagram is that your reservoir should be placed higher than your pump if possible. This way, air bubbles naturally float away from your pump. NEVER turn on your pump without first saturating it with liquid, because these pumps are naturally lubricated by the liquid instead of having oil.

Okay, now the first thing you want to do when installing a custom loop, is not install it. What you want to do, is sit back and take a look at your case, figure out a path for your tubing and where your parts will be located(res, rad, etc). Once you are 100% sure where everything is going, go ahead and screw your fittings into every part that requires them, and install them all into your case. After doing this, take your tubing and hold it up to the correct fittings. Each part should have some indication of which is the inlet and which is the outlet. Cut your tubing to the correct size using a pair of scissors or tube cutters. Try to keep the cut as straight as possible. Remember to leave a little extra tubing at each end for when you actually push them onto the fittings, it's better to have a little too much tubing, than not enough.

Next, collect all your hardware and rinse it out. For your waterblock, tubing, and reservoir, this is as simple as just running some distilled water through it and dumping it out. Your radiator, however, is a bit more complicated. Radiators can often come with a bit of debris left over from manufacturing inside, so you'll want to give it a very thorough rinse before you hook it up. To do this, heat up some distilled water and pour it into your radiator, filling it up about two thirds of the way. Plug up the holes, and then shake it vigorously for a minute or two. Dump the water back out into a bowl, and you may find that a lot of debris comes out with the water. Repeat this process until the water comes out clear.

Now that everything's clean and ready to go, install your main components. The waterblock will mount to your CPU the same way any other cooler would: Add a small dab of thermal paste to the CPU, set the cooler on top, attach the backplate to the back of your motherboard, and screw it into place. When you screw it in, make sure to only give each screw a few twists at a time, moving in a star pattern so that pressure is applied evenly to your processor.

If you have a big enough case, you can mount the radiator just by mounting it on the vent your fans usually go, then screwing the fan to the radiator itself. If you have a larger case, you'll likely mount it in the bottom. If neither of those are an option, you'll need to mount it externally using the brackets that come with it.

Mount your reservoir and pump using velcro or the mounting hardware that come with them. If you have a bay reservoir, just slide it into place and screw it into the sides like you would a DVD drive.

Now that everything's in place, it's time to connect it all with your tubing. Screw your fittings into each component, making sure they're good and tight before you continue so you don't spring a leak. It's good to screw them in finger tight, then give them a small turn with a wrench or pair of pliers to make sure they're snug.

Now, start connecting your tubing. Slide one end of your tubing over a fitting, then measure how much tubing you'll need to connect it to the subsequent component in the loop. Mark it with your finger, and cut the tubing with a pair of scissors. Cut it as straight as you can. Connect that end of the tubing to the next component, and repeat this process with each piece of hardware. Make sure you're connecting the tubing to the correct fitting each timeyour blocks, pump, and reservoir should each have a designated inlet and outlet. It won't matter which holes you use on your radiator.

You may find during this step that the tubing makes too sharp a turn, and kinks. This is bad for your water flow, so you need to return to the planning stage and see if there's a way to make that bend without a kinksometimes giving yourself some extra tubing solves the problem, but other times you'll need to connect your components in a different order. To disconnect tubing from your fitting, you may need to slice it with a razor blade where the two connectpulling them off is often very hard to do.

Lastly, if you're using barb fittingseven if your tubing seems like it's on snuguse hose clamps or zip ties to secure them! You can never be too safe and what's a tiny bit more money when it makes your loop so much safer?

Okay, so now we're nearly done. It's tie to fill your loop with coolant. This can be done outside the case first but that's no real benefit and just wastes time, you can still spring a leak moving your loop to inside your case after testing it outside. Make sure to go very slowly and correctly, don't rush anything and you shouldn't have a problem. Also, make sure to put some paper towel down inside your computer, and if you do spring a leak, plug it up, empty out your loop, and give your computer 24 hours to dry off. Most of your hardware will be fine, even if you get a little water on it. This is when non conductive coolant comes in handy.

Before you fill up, you'll need to jump your power supply. This lets you test the pump and the fans without actually turning on the computer itself. Disconnect the 24-pin cable from your motherboard, and connect the green wire to the black wire using a paper clip.

Next, add your liquid additives to your water, if applicable. Grab a funnel and put it in the reservoir's fill port. Carefully pour your water in, filling the reservoir almost to the top. Some may empty into the tubing, which is okay. Once the reservoir is filled up, flip the power switch on the back of your computer and let it run for a second. When your reservoir gets about halfway down, turn the computer off before the pump runs dry. It's very important to make sure your pump never runs dry, as this can permanently damage your pump in a matter of seconds. Once you've let a little water out of the reservoir, fill it up to the top again. Repeat this process until the water level in your reservoir stays constant. Double check your loop for any leaks, and if everything's okay, you have yourself a working water loop!

You're finally here, the end of your installation. This is the last step. You're going to want to let your loop run for at least 24 hours(seriously). Leave it running and check back every so often to make sure all is well. During these 24 hours, you should also find that a lot of the bubbles in your loop will bleed out. You may need to tip, shake, or jiggle the case to help this process along, as well as tap or pinch the tubing. Don't worry if you have a few small bubbles left over, they'll go away in time. A drop or two of dish soap can help bleed out the bubbles as well.

Once your satisfied that everything is leak free, you're good to go. Turn the PC off, connect everything back up properly and you're good to go.

Rigid tubing will give you a straight run which may look nicer and it is less likely to discolour than other tubing. However, it will be harder to upgrade, swap components and/or move stuff about. There's next to no flexibiity so your bends have to be specific and it's a little more expensive to set up rigid tubing than it is to just use regular tubing.
[ Register or Signin to view external links. ]
That is an example of rigid tubing. Notice how the tubing haas been bent in to shape.

Flexible tubing will be cheaper and you don't have to be precise with bends/connections or use heat to bend the tubing into shape. However, it doesn't hold it's shape, obviously, it's flexible and some people don't think it looks as nice as rigid tubing does. I personally prefer the look of flexible tubing.
I'll use an image of an AIO cooler as an example of flexible tubing.
[ Register or Signin to view external links. ]
Notice how the tubing just curves into position and sags slightly.