They have given small comfort amid a sea of painful memories in the 15 years since Brett Ponting, a profoundly disabled man, was left unsupervised to drown in the bathtub of his government-run group home.

The death threw Ms Ponting head-first into a long and very public fight to change the ACT's disability-care system, which she hoped would bring about lasting change.

But revelations of a similarly preventable death, that of Stephanie Fry in 2011, have made her fear the lessons learnt have already been forgotten.

"It makes me feel very angry, it makes me feel that Brett's death was in vain," Ms Ponting said.

"The fight that I took on on his behalf was all about him and the other guys and women that were at-risk in that system."

"The system is still failing, the management is still failing."

Mr Ponting's death was one of three in 1999 and 2000 in government-run homes, and helped spark a major inquiry led by ACT Supreme Court Justice John Gallop.

He found, among many other problems, serious issues with staffing continuity, induction processes, and the system's reliance on casual workers not familiar with residents' needs.

Those problems again reared their head in Ms Fry's death 10 years later, when unfamiliar casual workers on their first shift failed to heed a warning that she was not to be given bread or eat unsupervised.

Mr Ponting was left unsupervised in the bath, despite Ms Ponting earlier that day telling a support worker new to the group home to make sure he read her son's individual plan.

His file contained a warning - similar to the warning not to give Ms Fry bread - that he ought not be left unsupervised, including in the bath.

The next time Ms Ponting saw the worker was at Canberra Hospital, having just watched her son wheeled past her into the emergency room, cold and blue.

"I said 'I just want to know one thing from you, was Brett alone in the bath?' And he said 'yes'."

"And I said 'that's all I need to know, now I just want to go and see my son'."

Ms Ponting still remembers giving her son two of his favourite things – balloons and the song Raindrops – before making the agonising decision to turn off his life support.

"He just took one breath and he went," she said.

She also remembers her "complete anger" and the vow she made to seek justice and change.

Now, 15 years later, she fears the same failings that tore her life apart are still being allowed to destroy the lives of others in the system.