In the present study, the damage mechanisms that cause premature failure of sapphire water jet orifices were analyzed using a combined experimental and finite element modeling (FEM) approach. Depending on the operating behavior and local conditions, the service life of orifices for high-pressure water jet cutting often deviates considerably from the manufacturer’s specifications. Literature states a typical service life of 50 to 100 h, while in some cases, premature failure after a few hours or even minutes of operation can be observed. The focus of this paper is on the interaction of particles that impact the orifice surface but also the effect of faulty orifice assembly is taken into account. To estimate the risk of failure, the stress distribution in critical parts of the orifice were calculated via FEM, which is fed with experimental data. The modified Mohr failure criterion was then used to evaluate the stress distributions with respect to the possible failure of the orifice jewel. The results revealed that the risk of damage caused by excessive assembly preload forces is marginal. The stress caused by the impact of particles of different sizes is up to four orders of magnitude higher than the stress caused by assembly forces and is therefore identified as the main risk for orifices to fail prematurely. Experimental data shows mainly particles of calcium carbonate and iron–aluminum silicates, which are compounds that originate from the process water itself. It is demonstrated that particles are more critical than formerly assumed in the literature. This paper identifies particles with a diameter of more than 10 µm as critical when there are no other loads present. In operation, even particles as small as 2 µm in diameter can cause damage to the orifice jewel. To prevent premature orifice failure due to foreign particles, water filtration with a 2 µm mesh is recommended, while future research needs to focus on the interior cutting head design to prevent precipitation from the process water.