Labour MSP, Rhoda Grant, is writing to Scottish Water after the utility firm halted upgrade works in Harris at the last minute.
Water treatment plants plus a new mains pipe line between Tarbert and Hushinish were due to be replaced.
Scottish Water said reviewing the project due to soaring costs.
Rhoda Grant said she understood “such costs would have been understood prior to this point and indeed prior to engaging the contractor.”
She added: The cancellation of these works is now raising fears that outlying area projects may be getting dropped in favour of investment in other more urban areas.”
A Scottish Water spokesperson told Hebrides News: “We had originally intended to hold public events last week to inform residents in North Harris about work that was planned affecting their water supplies.
“This would have involved the replacement of four small water treatment works with a connection to the water network serving Tarbert.
“Due to a significant increase in the expected cost of the work, we are reviewing the options to continue providing a safe, reliable and affordable water supply for our customers in the area.
“The information events were therefore not able to go ahead and we will provide an update on our plans later in the year once the review is complete.
“We would like to apologise to customers for any inconvenience caused by the cancellation of the events.”
Scottish Water criticised for stopping Harris upgrade
25 March 2017