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It was postulated by J. Montesinos et al. (see ibid., vol.9, p.236-43, 2002), based on experimental evidence, that brittle fracture failures of composite (non-ceramic) HV insulators could be caused by water and mechanical stresses. It was also claimed therein that the brittle fracture process was more likely to happen with water than acids. This postulation could be of major importance as its ramifications might affect the entire composite insulator technology and, in particular, the usage of glass fiber polymer matrix composites in HV applications. Such an important statement should not be left without an independent verification. Therefore, attempts have been made in this research to initiate this process in unidirectional E-glass/modified polyester and E-glass/vinyl ester composites, used in non-ceramic insulators, by subjecting them to water under four-point bending conditions. This was done to independently verify the main conclusion of J. Montesinos et al. that water may be more damaging to unidirectional E-glass/polymer composites than acids. It has been clearly shown in this work that water, in the absence of electrical field, cannot cause stress corrosion cracking of unidirectional E-glass/polymer composites and thus brittle fracture of composite non-ceramic insulators. Thus the main results of J. Montesinos et al. could not be independently reproduced.