Water cooling is good if you maintain the system. Just like an automobile, you need to check the fluid and ensure there is enough coolant in the system otherwise the water will remain warm and not cool the system enough or at all. There can also be a problem with algae build-up so a good algaecide has to be added to the fluid whenever the system is topped off. There are also problems with leaks, as my brother-in-law found out the hard way. It didn't do any damage, but it sure caused an awful mess to clean up. His problem, by the way, was self-inflicted and caused by poking around in the computer case.
Blowing directly on the components...
This will work to a certain point, but then there is the ambient air issue because the fan is doing nothing than moving the air around as the internal components can't push their heat away from them. Unlike human beings and other warm blooded critters, computers don't sweat so there is no wicking of moisture to cool things down. Most computer cases are tight with air vents placed in such a way that the air flows across the surface. The in-blowing fans force the air across the components quickly due to the Bernoulli effect; the same reason why wind pulls people out from under bridges in severe storms... This increased air flow moves the hot air away from the components and cools them down.
Some components, such as CPUs and GPUs, use what is called a heat pipe. This is a fan placed very tightly on a big heat sink which forces the heat out of the case in a similar fashion. You find these a lot in laptops and other devices that have a tiny space, including video cards. On big servers and workstations, there are direct pipe-blowers placed on the CPU and sometimes the video cards. These also work in a similar fashion, however, they make use of more commonly available fans, but requite some kind of plastic or cardboard box around the fan and CPU.
The best solution for cooling is adequate airflow overall, which of course you are implying here with the big fan placed in front of the system. To ensure proper airflow, there are steps that are needed that ensure there is nothing in the way to impede the air. With more and more components being crammed into smaller computer cases, we have problems with wiring and cabling. case components, and other things getting in the way of proper air flow. With the more common SATA devices and rounded cables, the cabling has become less of a problem, however, that doesn't solve hard drives, and yes even SSDs are placed in hard drive-sized boxes, or other power cables needed to power up the motherboard. For this issue, I have run the power cables and extraneous wires behind the motherboard support plate, against the back cover of my computer case. The particular case I have, a Corsair 650D also has wire guides and rubberized holes so that all wires are run outside and away from the boards, making an extremely open case inside.
Cases should also be large enough to support both the wiring and cabling as well as have room for all the components...
In the past, I dealt with some DEC 300 workstations. These machines were so tightly packed, the hard drive magnets actually affected each other in a dual-drive system! The service techs were constantly replacing hard drives and CPUs in these machines. The drives because they would magnetize each other and die, and CPUs because they would cook. Literally cook. The machines got so hot inside that the case was hot enough to keep a cup of coffee warm on the top!
There needs to be more than one fan...
In addition to the fan blowing in, there should be one or more fans venting out. These when strategically placed, will pull the air away from the components. What you don't need is air pushing in against the components with no place for it to go. This can actually impede to cooling of the components as there is nowhere for the heat to go.
And finally...
You need to keep the system clean inside. With the fans sucking in air, there is sure to be dust along with it. Keeping the computer clean inside ensures the components stay cool as dust clogs their heatsinks and fans, and prevents the air from flowing properly. Periodically remove the dust from the components and fans by using compressed air, not a household vacuum! Compressed air from a can will work well, but just remember to put a drinking straw or some small stick into the fans to prevent them from spinning while applying the air to them. Without this additional step, the forced air can damage the bushings inside the fans. And, as I said, never use a household vacuum. These devices can build up a dangerously high static charge which will damage the electronic devices inside the computer.
John