TasWater say it is working through a “thorough program” to find out why a water treatment plant at Deloraine failed to treat water properly.
The incident occurred on Friday and a boil water alert has been in place since.
The town’s whole water supply was affected.
Water samples are being analysed to determine if the contaminants have been flushed out.
Once the assessment is clear, and the Health Department are satisfied, the boil water alert will be removed.