This work studied the effect of composition of powders and water content on mixture quality (MQ) of three binary powder mixtures with good (salt/paprika or salt/sugar) or poor mixing (salt/oregano) behaviour. The mixing behaviour was assessed using coefficient of variation. Results showed that mixture composition did not influence the MQ of sugar/salt and paprika/salt within 20–80% salt content range but it did influence the MQ of oregano/salt with a progressive dis-improvement in MQ with higher oregano content and also for low concentrations of 1% salt. Water content did have an effect on mixing behaviour. When paprika with high water activity (aw) was mixed with salt, the time required to reach good MQ was longer because of the increased cohesiveness and when oregano with high aw was mixed with salt it displayed improved MQ because salt particles were able to stick onto the larger oregano particles and reduced segregation.