do i need liquid cooling for overclocking

Solution

Water cooling is 100% not needed, unless your trying to squeak the last 0.2 out of your processor that most people don't try to do anyhow.
Drawbacks of water cooling, the obvious possibility of a leak killing your PC parts (rare but does happen) also if you have a pump failure your PC is 100% down till you can replace it.
High end air cools just as good as a 100 buck water cooler, so close it don't matter and if you have a fan failure you can just swap it out with a case fan till you can get a new one and keep using the PC.
My experience with AIO water had a 3 year old H100 decided to change it before I had pump problems and bought a Cryorig R1 air cooler and it lowered...
No, you don. t need watercooling for overclock. However depending on the cpu and depending on the clocks you want to reach, you might want to consider watercooling in order for safer temps. But you can easily overclock without watercooling.
 
hemant_5,

Water Cooling can be really expensive, depending on the type of loop.

Custom: A DIY loop, connecting anything that you can buy a water block for e.g (RAM,CPU,GPU,Northbridge)
Custom are really expensive, and rarely done for their cooling efforts. Although they are very good at cooling hardware, the purchasing of radiators,water blocks,tubing, and fittings can make a VERY inefficient Cooling to Cost ratio.
I dont recommend for you to make one.
Example:http://www.newegg.com/Product/Product.aspx?Item=9SIA6ZP3S84225

AIO's: Standing for "All In One's" are prebuilt, water-cooling loops, that can be expanded on traditional only include a CPU water block with a pump, and a radiator. These offer a BETTER Cooling to Cost ratio, but can get quite expensive.
If you plan on Overclocking a lot, you may need one.
Example: http://www.newegg.com/Product/Product.aspx?Item=N82E16835181090&cm_re=H100_GTX-_-35-181-090-_-Product

AIO-Hybrids: Are just like AIO coolers, and usually come prebuilt with a pump/reservoir,CPU block and radiator. They are quite expensive but can be worth it as they allow for expandability.
These can be a cheaper way of making a custom loop.
Example: http://www.ekwb.com/predator/

Water-cooling is for serious Overclock's.
If you just plan on trying Overclock, and aren't even sure if you've got a lucky chip, just go with a cheap air-cooler like this:http://www.coolermaster.com/cooling/cpu-air-cooler/hyper-212-evo/
The Hyper EVO 212 is great for Overclocking starters. If you find you need more cooling, you may want to invest in one of the above, water cooling options.

If theres anything I missed, just ask

~Nnokalad
 

Water cooling is 100% not needed, unless your trying to squeak the last 0.2 out of your processor that most people don't try to do anyhow.
Drawbacks of water cooling, the obvious possibility of a leak killing your PC parts (rare but does happen) also if you have a pump failure your PC is 100% down till you can replace it.
High end air cools just as good as a 100 buck water cooler, so close it don't matter and if you have a fan failure you can just swap it out with a case fan till you can get a new one and keep using the PC.
My experience with AIO water had a 3 year old H100 decided to change it before I had pump problems and bought a Cryorig R1 air cooler and it lowered my temps a few C.
I would very highly recommend their products.
http://www.cryorig.com/product.php

 
Solution
Agree with the posts above
In summary, The better the cooler, the more you can raise your CPU Vcore voltage.
The more you can raise your voltage, the faster you can go.
But too much voltage reduces the life of the CPU.
So if you need a water cooler, you are probably harming your CPU.
AND even at high Vcore voltage there is no guarantee of a big overclock, because some CPU are dogs and are not stable at a big overclock no matter what you do.

I am using the stock cooler, at slightly below stock voltage, to get a small overclock for free. (see signature)
I could probably have gone 10% faster, but it would have cost me $$$$ for a better motherboard and big cooler, which is not worth it IMHO