Residents using the municipal water supply along part of William Street in Tavistock are being advised to boil their water after a main break caused a loss of pressure that may have compromised the system. Southwestern Public Health issued the advisory after the Medical Officer of Health was notified that a water main break occurred near 168 William St. on May 7. The advisory applies to properties on William Street south of Wettlaufer Street and is being issued as a precaution against possible contamination. Affected residents are being notified by the County of Oxford and will receive further notice when the advisory is lifted. Medical Officer of Health Dr. Ninh Tran is advising those impacted to bring all water to a rolling boil for at least one minute before use. The precaution applies to drinking water as well as water used for brushing teeth, preparing infant formula or juice, washing raw foods and making ice. Health officials say the advisory will remain in place until testing confirms the water is safe to drink.