Passers-by mainly ignore me, a homeless woman sitting on the sidewalk or a bench. The people who do speak to me are either curious, or harpies who give me unsolicited and useless advice, or the more irritable who chastise me. I try to explain by example that there are good, decent, employable but destitute people in New York City.

Many people also assume that the homeless are all drug addicts, criminals or prostitutes. I am none of these things, yet I have seen the stereotypes first-hand.

I try to keep busy, doing whatever jobs I can find, often the kinds of jobs illegal immigrants now do. When I volunteered at a church soup kitchen, hoping to do my part, a stranger claimed all these nasty things about me in the presence of the minster and other members of the church. For years, she continued to make these sorts of remarks and warned new volunteers that I would steal from them. No one said a word in my defense.

I don't have recent data, but I know that in 1994, a study of homeless people in Manhattan was published and a summary appeared in many New York City newspapers. The findings said that 30-40% of the street homeless population suffered from a mental illness, including alcoholism and drug addiction. It's a tragic statistic, but you can also infer from this survey that 60-70% of the street homeless are not mentally ill, drug addicted or alcoholic. People should remember that other factors – such as education, job training, employment, the housing market and how programs for the poor are administered – also cause people to end up on the streets.

It's very painful for me to talk about how I ended up homeless. I will not get into all the specifics, but I lost my job and that spiralled into losing my rent-controlled apartment. I went to the city for help and was given a list of charities to contact. I reached out to all of them, hoping one could give me the money I needed to pay the rent. It was only $400, but no one would help.

One thing led to another and now it is difficult to ever imagine getting back into any sort of stable job. I have gaps in my resume. I have no permanent address or bank account. Landlords want to see evidence of stable income.

I am often asked if I have enough to eat. I will eat anything that is healthful. People who work with food bring leftovers to me. Once a week, I help unload a farm truck because the food co-op members are not there when the truck arrives. The drivers give me delicious fruit many times. I also sweep a pavement outside of a restaurant, and the owners give me hot soup in the winter. Kind people will buy hot coffee and a bagel, sometimes pizza for me. Around the holidays, people will drop off homemade cookies and other gifts.

Prepared food cannot be purchased with food stamps. For homeless like me, without a place to cook, this eliminates cooked vegetables and any other hot food in the winter. An alternative is soup kitchens. The volunteers work to make it peasant and serve edible food. I thank them. But sometimes, the food is filling, but not nutritious. Starches like bread, cereals, pasta and rice are the main components of most meals.

Relying on soup kitchens to eat also means most of the day is spent zig-zagging around town, standing in long lines and filing into overcrowded seating areas. There are many people with poor table manners, unhygienic habits or looking for a fight. If you want the truth, shelters, soup kitchens and other facilities for the poor are the most unsanitary, unhealthy and dangerous places I have ever been.

There is often not enough food to feed everyone in shelters. Once, a woman had a bad cold in the shelter I was staying at, so I bought three dozen oranges to share. For doing this, I was reprimanded by the staff and a social worker. A long-time tenant of this particular shelter explained that NYC was paying to feed us three daily meals and an evening snack. But this was not being done. A week later, boxes of food were delivered, and several boxes were taken by the staff as they left that night.

I have seen some of the best and worst of humanity since I became homeless a few years before the recession. My belongings have been stolen by other residents and workers at the shelters and even church personnel and pedestrians. One time, a shelter worker threw out the books belonging to the local library, causing me problems trying to get anything else from the library. Another time, my purse, which I kept inside a backpack, was stolen. It contained a lot of information about friends and relatives and other personal papers. You cannot replace those.

The worst are the showers for the homeless. At the shelters for women, all of the bathroom doors were adjusted to assist in monitoring for smoking, drug use and potential suicide. For about 150 women, there are often only two showers and only a few hours when they are available. So a list gets made, and those on the list monitor the use of the showers, announcing who is next and reminding her to be quick. Just as soon as a woman enters the shower stall, another woman starts yelling for her to hurry up. The complaints escalate down the line of those waiting.

Soon, they call over to the male shelter worker (I don't know why men are allowed such a job) that the user is past her time limit and he should make her get out. The male workers yells from his desk, knocks several times on the door and then unlocks the door and opens it. Almost always, the shower user has not finished dressing and can be seen in plain view by many other people. If she shouts with embarrassment and indignation, the male worker will shout back admonitions and threats to call the police on her.

I don't want to sound like I am whining. I have also met people like a young woman who saw me upset after an attack by a resident of the Park Avenue women's shelter. She approached me and asked me what was wrong. I told her that I had put down my bags to rest and a complete stranger came screaming and raging at me. When I backed away, she threw my bags in the street. I have no idea why. Was this woman crazy or just angry that a homeless woman would be on her block?

When she walked away, I retrieved my bags, but she returned and continued the same behavior. Finally, she left, and I got my bags. The young woman asked if she could help me. I told her how I had lost my apartment, what the shelters were like, and previous work I had done. She was focused, patient, a good listener and gave me cash.

The young woman's unselfish behavior mitigated an unpleasant experience. Her compassionate heart and generous spirit allowed me to walk away fresh. She was exceptional, although other people I have encountered have demonstrated some of her qualities of character.

My dream is to be a middle school math teacher. My college degree is in computer science, and I used to be a substitute teacher. I know this probably won't happen. For now, I do what I have to. I just wish people wouldn't make assumptions about me, especially that I am crazy or a criminal.

• Editor's note: Mary often sits on the same block as a Guardian editor. This piece was compiled from Mary's handwritten notes and many conversations with the editor. Mary was paid a similar fee to other Guardian contributors