Water is a solvent. It has numerous properties that set it apart from other solvents. The basic one is its property of surrounding different ions so that molecules break into separate charged entities within it. However, this property of breaking up molecules into ions is also dependent on the property of the solute. If it is a strong solute, the water will surround all the different ions making it fully ionized.
However, if the electrolyte is weak, it means that the molecule tends to stay in its non-ionized form. Hence, few ions will form. This chemistry applies to all electrolytes.