There is always a chance for water to leak, ALWAYS!
Unless of course you don't use a water based cooling system.
For my $0.02, the only good thing about the low end watercooling kits (for the average home user/gamer) is the bragging rights you get because you can say you have watercooling. I say this because for similar money you can get a high end (air) heatsink with similar cooling performance.
If the fan on an air heatsink fails - you still get decent passive cooling performance due to the mass of the heatsink/fans/heat pipes.
If the pump on a water system fails - you don't hear it, don't (usually) get a slow fan warning from the bios, and with so little water sitting in the waterblock on the CPU - it overheats in no time and has awful 'passive' performance.
As I said, only my $0.02... I know there are many here who think the cheap watercooling kits are the best thing in the world for home users, but I'm clearly not one of em 😉