Surfactants are commonly employed in numerous industrial applications and everyday products due to their enhancing wetting abilities. Trisiloxane surfactants in particular have proved to be matchless in reducing the surface tension of the liquid and consequently in enhanced wetting on even highly hydrophobic surfaces. In many practical applications trisiloxanes are frequently used as water-based solution. For convenience and reduced cost they are often pre-mixed with water and left for long periods of time in aqueous environment. We provide evidence that ageing of trisiloxane surfactants in water solutions may lead to loss of their interfacial activity. A mechanism for the observed behaviour is suggested and the phenomenon quantified. Along with a detailed explanation of the problem, we shed light on the dynamics of the process and provide some limitations of pre-mixed solutions.