Locked doors, a whiff of urine and a cacophony of television noise herald the clinical "day room" where a huddle of humans slump uneasily in chairs. One is Mary Delaney, a 78-year-old widow with six children scattered across England and the Americas. She is in the early stages of Alzheimer's.

She was a trained nurse, forced to give up by the marriage bar; a practical kind of woman who, while rearing her children and supporting her husband, kept a fine vegetable garden, visited the sick and laid out her neighbours' dead. She used to be addressed as Mrs Delaney and referred to her neighbours in the same respectful way.

Today, a robust care assistant barely a quarter of her age gives her a playful slap and trills: "This is Mary - she always looks like someone's going to batter her." Later, the matron points to Mary as she approaches and booms, clear as a bell: "Here's another Alzheimer's . . ."

Mary looks agitated. In her dementia, the cacophony of noise is unbearable. A dripping tap will sound like a lawnmower.

Here, in a south Dublin nursing home, all traces of Mrs Delaney and her hard-working, hospitable and generous life are slowly being obliterated. No clothes to wash nor a line to peg them out on; no garden to hoe and nurture; no walks to the neighbours' or chats with the postman; the familiar view from her kitchen window and the big old family dog are lost to her for ever. The woman whose automatic response to visitors was to put the kettle on is now barred from the kitchen, unable to offer something as basic as a cup of tea without petitioning a busy staff member. The few photographs in her room are all that remain of a good woman's life. Her children come when they can, in the summer and at Christmas.

Some of it can't be helped, but much of it could. The matron nods thoughtfully but can see no solution. She sticks to the rules and passes muster with the health-board inspectors. The whiff is unavoidable at times, she says, and her residents clearly are warm and well fed, and have good medical care. But do they have a life?

"There's very little you can do," says the matron. "We have sing-songs and bingo. There's the television and the papers if they want them." Could they make a cup of tea? "You couldn't have people in that condition around boiling water - it's against the Health and Safety Act. This is not an occupational-therapy centre." The Health and Safety Act: it trips easily from the mouths of those who pride themselves on running a tight ship.

It's not much of a life on this tight ship, but at least they get their tea in china cups. A colleague of mine who was searching for a place for her mainly lucid, medium dependant father found private nursing homes in Dublin, costing £500 to £600 a week, where stainless-steel soup bowls and plastic cups were deemed acceptable.

Behind what were often charming reception areas for prospective clients and their families, she found a much bleaker reality. The huddle of misery described above was horribly familiar. She remembers one place with frail second-floor residents had no obvious alternative to the stairs. One place had two toilets for 20 people, and one of those was out of order; another had one shower for 10 people.

"OK, it's possible that I was being too picky," she says, "but I couldn't bear to take a chance if there was the slightest hint that everything wasn't right. It's such a huge decision and you're so raw, all you can do is follow your instincts. If, as I found, a nurse is giving people little slaps on the arm with the kind of patronising attitude that says, 'You silly little thing, run along now', in front of visitors - well, you have to wonder what goes on when there are no visitors around. I found it shocking and worrying."

Was she being too picky? Mindsets matter. A care worker in a nursing home where most of the residents have dementia says it's not unusual to see residents left on commodes in full view of others. "They should have a screen put around them, but when it's busy they might not. Sometimes you'd see people restrained in a chair with the belt of their dressing gown, and no one bats an eyelid. I'm not saying these old people are easy - they can be incredibly selfish and aggressive, and you mightn't get a 'thanks' out of them in a month of Sundays. But a lot of them are just very depressed and vulnerable."

In any case, you can never assume that people with dementia are incapable of insight. Mary Drury, the education officer for the dementia-services centre at St James's Hospital in Dublin is a zealot on this point. She quotes a passage from John Bayley's memoir of his wife, the novelist Iris Murdoch, to illustrate that even someone for whom the Teletubbies have become the sum of life can occasionally emerge from the fog. After one of Bayley's savage recitals of despair on their predicament, delivered, as he thought, to an uncomprehending audience, Murdoch suddenly turned to him and, with perfect understanding, said: "But I love you."

My colleague is at one with Drury. "There seemed to be a lack of understanding about what happens to people as they age. If people couldn't talk coherently, it seemed to be automatically assumed that they were no longer cognitive and didn't either hear or understand what was going on around them. Everything I saw led me to believe that in fact the opposite was the case. My father could pick up every nuance of behaviour or conversation of people with him, although he might have difficulty making a coherent sentence."

The point about this treatment of dementia is important; more than half of those in residential care are affected by it. By 2025, it is estimated that 52,000 of us will have some form of dementia. But who wants to see a beloved parent reduced to eating out of a tin dish like a dog, and what does it reveal about the mindsets of those who run such places? If incontinence management depends on toilets being close and in clear view, how can any nursing home justify having only one for 20 people? Will a place with one shower for 10 people ensure that its residents have a wash every day?

Or is there a feeling that these are sick old people who are going to die anyway? Mindset is vital, because it taints everything it touches.

In many nursing homes, staff are institutionalised in attitude and outlook, and the routine rules. Stimulation and quality of life for their residents come bottom of the list - if they are in there at all. "Stimulation is the ongoing battle," says a senior health-board official. "The health boards ran a series of seminars for nursing-home staff to address the problem. But some just aren't interested; some are, but don't know how to go about it; and some are unwilling to pay."

It seems nursing homes have enormous leeway and discretion on such issues. Yet the Department of Health and Children's 1995 code of practice for nursing homes states: "For the more dependent residents, opportunities for social interaction should be encouraged to the limit of the person's ability. Reorientation and reminiscence therapy are a valuable way of encouraging this interaction.

"Responsible risk-taking should be regarded as normal and residents should not be discouraged from undertaking certain activities solely on the grounds that there is an element of risk. Excessive paternalism and concern with safety may lead to infringement of personal rights."

It also states what seems dazzlingly obvious: "Staff should be aware of the individual's identity and their past achievements."

Among a sample of nursing homes surveyed for a review of the government policy document The Years Ahead, nearly a third had never heard of the code of practice. It remains voluntary. The matrons and staff who are caring, open and willing to learn have little need of it; those who are not see no need for it.

Crucially, there is no law to make them see, even while entrusted with the State's most vulnerable, invisible citizens.