The mother of a 10-year-old girl who died at a Glasgow children's hospital claims she was "let down and lied to" by health officials.
Milly Main contracted an infection in 2017 while recovering from leukaemia at the Royal Hospital for Children.
Her mother told the BBC she was "100%" certain contaminated water caused the fatal infection.
Greater Glasgow health board insists the source of the infection cannot be determined.
Kimberly Darroch gave details of her daughter's case after it was highlighted in the Scottish Parliament on Thursday, prompting calls for the resignation of Health Secretary Jeane Freeman.
Ms Darroch said she emailed Ms Freeman in September "asking for answers" about her daughter's death but received only general assurances that it would be considered as part of an official inquiry.
Ms Freeman said she instructed officials to get in contact with the family and did not make a public statement out of respect for patient confidentiality.
Milly's mother described breaking down in tears when she read in the Daily Record newspaper on Thursday that an unpublicised clinician-led review had identified 26 infection cases in 2017 possibly linked to contaminated water on the cancer ward - including one that led to the death of a child.
"I feel let down but lied to. I don't know how to put it into words. There are no words to be honest I'm in shock, complete shock with it all," she said.
Milly, who had leukaemia, underwent a successful stem cell transplant in July 2017 and was making a good recovery when the following month her Hickman line, a catheter used to administer drugs, became infected. Milly went into toxic shock and died some days later.
Her death certificate lists a Stenotrophomonas infection of the Hickman line among the possible causes of death but Ms Darroch says the family were kept in the dark about a potential link to contaminated water problems at the hospital.
She said shower heads were changed in the months before her daughter's death, and she is convinced the water supply was the source of the infection.
"I think they knew prior to Milly's death that the water was contaminated. I feel they knew this was the infection that killed my daughter but no-one came forward to tell us."
She added: "If they had told us at the time it would have been a hard pill to swallow but I would have swallowed it if they had just been honest."
In September she emailed the health secretary asking for answers about her daughter's death.
"I emailed Jeane Freeman and got a reply 10 days later saying they would look into it and get back to me.
"They did get back to me a number of weeks later with a generic letter. It was addressed to myself and was slightly personal - but not very personal - saying they were holding an inquiry and they would pass it on to the health board's complaints manager. "
Asked what she wanted to happen next, she said: "I think they should get the answers from the inquiry and release them. I want an apology. I want them to admit what they've done is wrong and I want them to admit that they've covered it up."
'No way to know'
NHS Greater Glasgow and Clyde said at the time there was no requirement to test the water supply for Stenotrophomonas.
In a statement it said: "We have offered to meet Mrs Darroch to discuss her concerns, and to answer her questions where we can.
"We fully understand that the family wants to know whether the infection Milly had is connected to the water supply.
"The truth is there is no way to know this as we did not consider this to be the source at the time and we did not test for the particular infection in the water supply."
Health Secretary Jeane Freeman said the email from Milly's mother in September was the first time she was made aware of the child's death.
She said: "On 23 October I wrote to the parent expressing my condolences for their very sad loss and I would like to again take this opportunity to do so.
"I also advised them that I was ensuring that senior staff from NHS Greater Glasgow and Clyde would make personal contact with them to address the questions I was sure they would have.
"Following my intervention I have checked and been assured that communication has been established, which will provide the necessary information for the family.
"I also made clear to the parent my intention that the public inquiry will be an opportunity for the voices of families to be heard and for answers to be provided.
"I am at all times aware of the importance of patient confidentiality and so, rightly I believe, I did not treat this correspondence as a public matter."
The problem of contaminated water is one of a number to beset the Queen Elizabeth University Hospital (QEUH) and the adjoining Royal Hospital for Children.
Last year two cancer wards at the children's hospital were shut because of concerns about infection, and children were moved to the QEUH instead. An inquiry by Health Protection Scotland later identified 23 potentially water supply-linked infections during 2018.
In January it emerged two patients at the QEUH had died after contracting an infection linked to pigeon droppings.
Ms Freeman recently announced a public inquiry into construction issues at both the Glasgow "super hospital" site and the new children's hospital in Edinburgh.
'Milly's family deserve answers'
Scottish Labour MSP Anas Sarwar raised Milly's case at First Minister's Questions after a whistleblower revealed an unreported clinician-led review had identified 26 possible water supply-related infections in 2017 at the children's hospital.
Mr Sarwar said: "Milly's family deserve answers. It's the health secretary's job to protect patients and the staff, not the institution.
"They deserve answers and they deserve the the truth and those NHS staff who showed bravery in coming forward to be whistleblowers deserve to be protected."
Scottish Liberal Democrat health spokesman Alex Cole-Hamilton said Ms Freeman's decision not to go public was "incomprehensible" and called on her to make a statement at Holyrood on the issue.
The Scottish Conservatives called on the health secretary to resign over the case.
Tory health spokesman Miles Briggs said: "Patients will be absolutely furious that such a serious failure has been covered up by this SNP government.
"The health secretary must apologise to the family and resign or, if she refuses, be sacked."