We use a simple electrostatic treatment to model recent experiments on quantum Hall systems, in which charging of localised states by addition of integer or fractionally charged quasiparticles is observed. Treating the localised state as a compressible quantum dot or antidot embedded in an incompressible background, we calculate the electrostatic potential in its vicinity as a function or its charge, and the chemical potential values at which its charge changes. The results offer a quantitative framework for analysis of the observations. (c) 2006 Elsevier B.V. All rights reserved.312155159