Residents in Corofin and Ruan are being warned not to drink water provided on the public scheme.
Clare Council has issued the alert due to the presence of an algal bloom in Inchiquin Lake.
The local authority says the recent extended period of dry weather, elevated temperatures and reduced water levels in Inchiquin lake have led to the growth of an algal bloom.
An estimated 1800 customers of the Corofin and Ruan Public Water Supply are affected – this also includes customers of the Killeen Group Scheme.
The HSE, Irish Water and Clare County Council says tap water should only be used for the flushing of toilets, flushing of internal house plumbing systems and laundry.
Bathing in the lake is also prohibited and farmers and dog owners are advised to prevent thier animals from consuming the water their.
Further information on the provision of water tankers is expected to be released later.
Separately The HSE, Irish Water and Clare County Council will meet to discuss water issues in the Kildysart area. Residents have been without supply for over a fortnight due to the level of maganese in the water.
