Froth flotation is widely used in the mineral processing industry. Froth flotation utilises differences in physicochemical surface properties of various minerals to achieve specific separation. Frothers are added to stabilise bubble formation in the pulp phase and to create a stable froth at the top of the cell. Froth structure and froth stability are known to play a significant role in determining the mineral grade and recovery. Froth stability is mainly depending on type and amount of the frother used, as well as on the amount and nature of the suspended particles. However, there are other parameters such as quality of water which are not yet fully understood. In plant practice, the recycling of process water (and very often of water from different sources) to reduce freshwater consumption is increasingly being common. However, using recycled water normally leads to the build-up of salts and surfactants in solution. Therefore, the effect of the process water chemistry on froth stability, and more in general on the metallurgical performance, is very important. In this study, the effect of water quality, including pH and type and concentration of salts (such as CaCl2, AlCl3 and NaCl) on froth stability and viscosity in the flotation of a sulphide ore was studied. The effect of NaCl was negligible, while CaCl2 and AlCl3 considerably increased the froth stability (and viscosity). This may be due to bridging effect of polyvalent metal ions between the ore particles.