Clay balls can be used as an alternative to natural pebbles in pebble matrix filtration, a method for drinking water treatment. These clay balls are subjected to stresses due to self-weight and overburden in water-saturated conditions. Although there are empirical relationships to evaluate tensile yield strength ($Ts$) of clay balls using Poisson’s ratio ($\mu$), diameter ($d$) of clay balls, and failure polar force ($Fs$), so far for such calculations the value of Poisson’s ratio has been taken from studies based on clay bricks. However, during ball preparation, if clay is mixed with other raw materials from industry wastes, such as saw dust or alum sludge in order to enhance the pollutant removal properties of the filter media, then the Poisson’s ratio of composite balls would be quite different from that of clay bricks. This paper describes a novel method for estimating Poisson’s ratio of composite clay balls by measuring vertical deformation using LVDTs in a uniaxial compressive strength (UCS) apparatus and lateral deformation using particle image velocimetry (PIV).