Water in Mexico City comes out of the tap in a variety of colours (yellow, rusty or earthy tints), flavours (sulphuric, chlorinated or metallic) and textures (muddy or gritty). Water that doesn't smell, taste or look funky, however, is actually more dangerous, for it can sucker people into believing that it's drinkable. In general, all those who have other options don't drink the tap water.

The quality of water supplied to buildings here has consistently been ranked at the bottom of any list of world cities. In addition, rusty pipes, mould and old water tanks made from asbestos (prohibited since the 1970s but still used in lower-income buildings) can add harmful substances to the water. Over time, poor quality water can corrode the pipes and eventually cause them to burst.

The water I need to replenish my bodily fluids and to keep myself clean is pumped in daily through an underground pipe that empties into a huge cistern buried underneath the patio. An electric pump located in the patio lifts the water up from the cistern and into the large plastic water tank located on the roof, which in turn channels water back down into the bathroom, shower and kitchen.

In Mexico City, water is not free and every two months I must pay for the water I use. My apartment produces its own hot water with a gas-powered water heater located on my terrace, and the gas must be bought from a private company that sends a truck each month to fill up a stationary tank on the roof with liquified gas.

The lack of free, publicly supplied quality drinking water generates great business opportunities. To have water to drink, I buy large plastic jugs of water from bicycles equipped with a platform in front that service the neighborhood. Although each jug is relatively inexpensive, paying for water to drink is an added expense that adds up over the year.

It is not only drinking water that people must purchase. While those living in higher-income neighborhoods get cheap, government-subsidised tap water, the poorest parts of the population have no plumbing and receive no water at all in their homes. Those who live beyond the reach of the city's water pipes must buy water from trucks (called pipas) that distribute water out of a large hose at an even higher cost. For those who have no access to hot water in their homes, or those who lack indoor plumbing, there exists banos publicos. These public baths, which are actually private businesses, offer individual and communal showers for a modest fee, Turkish baths and saunas (soapy massages offered by teenage boys cost extra).

A vendor prepares to fill his bicycle cart with jugs of bottled water to sell to owners of streetfood stalls in Mexico City. Photograph: Marco Ugarte/AP

Public toilets also represent a booming private business niche these days, especially in the most visited tourist sites of the city, where for a small fee you receive access to urinals or toilets with toilet paper handed to you when you enter (some WCs even operate like the Metro, with ticket windows and turnstiles). Being that most of these WCs and some of the banos publicos are not licensed, chances are they don't even pay for the large quantity of water used.

To get access to needed water, whether it is in the shower, toilet or in a glass, you must pay for it. Yet even if people in the city are willing to pay for their water, soon there might not even be enough to go around.

Hydration at a price

Mexico City uses more water each day than any other city in the world. With its own water sources overexploited, an increasingly large part of its water must be brought in from outside the Mexico City valley.

So when I turn on the tap in my flat, the liquid that flows into my sink now mostly comes from distant bodies of water. Given that Mexico City is a mile-high mountain valley, bringing water up and into the city requires some pretty heavy duty machinery. Beginning in 1951, the Lerma river, located in the Toluca valley about 40 miles (70km) from the city, was the first outside water system to be tapped for use by residents of Mexico City.

The Lerma waterworks located in Chapultepec Park, equipped with pumps and pipes that connected the city to this distant water source, was an incredible engineering feat, acclaimed by the federal government (even though dozens of workers were killed in the process) and graced by the world's first underwater mural – Water, The Origin of Life, by Diego Rivera. For decades, the Lerma contributed up to 15% of Mexico City's water. Over the last few decades, however, it has largely been sucked dry. What's left of this once-great waterway is forcefed 170,000 tonnes of toxic slime from the factories, industrial parks and irregular cities located along the banks of the river.

As the Mexico City population has grown exponentially, other water sources have had to be tapped to meet the increasing demand. And as its pipes suck up water from further and further away, its water costs have increased exponentially. The Cutzamala river, twice as far away as the Lerma, now supplies up to one-third of Mexico City's water needs. The fact that local communities are being deprived of their own water sources in order to service the capital is a cause of discontent.

The Mazahua Indians who have lived around the Cutzamala for centuries now lack access to their own river water, and violent protests have resulted. In addition, as water sources tend to be interconnected, by overexploiting the river to supply drinking water to Mexico City residents, the Chapala lake in the very distant state of Jalisco is drying up.

The Lerma waterworks in Chapultepec Park, Mexico City; graced by the sculpture Water: The Origin of Life, by Diego Rivera. Photograph: Kurt Hollander

Lack of rainfall and higher temperatures lead to lower levels in the main water sources outside the city (dams in Cutzmala have recently been as low as 30% of their capacity), and the quality of water pumped in from the bottom of these dams is poor. In extreme cases, such as the widespread death of fish due to increased temperatures, these water sources can be poisoned. Although Mexico City as a whole depends on Cutzmala for only 30% of its water, some areas, such as the Santa Fe neighborhood in the south of the city, depend completely on water from this source and suffer droughts when its water levels sink.

Pumping more and more water up and into Mexico City requires more and more electricity. To meet this increased demand, more and more dams have been built on the country's rivers. These dams monopolise the local use of the water and often force whole towns to move from their homeland, in turn leading to a flood of migrants into Mexico City. Many of the millions of urban land invaders in Mexico City over the past few decades are farmers who fled rural areas impoverished from an inadequate access to water.

The new, haphazard cities these forced immigrants have created creep up and cover the mountains surrounding the city, destroying the trees and forests that normally replenish oxygen and protect the soil from becoming unusable dirt and dust. The lack of trees in turn puts these areas at risk of flooding and mudslides that claim human lives each year. In addition, the new cities populated with millions of inhabitants that have sprung up around the periphery of Mexico City over the past couple of decades have put an added strain on the city's water supply.

Water has long ceased to be a free, readily available natural resource. Paying for a natural substance like water seems unnatural, which is perhaps why a good percentage of people and companies in Mexico City don't pay their water bills. If the city government should decide one day to end the subsidies and make customers pay the real cost of the poor quality liquid that comes out of their taps, blood would flow instead of water.

The demand for water in Mexico City doubles every 20 years, twice as fast as the population growth. For each square metre of new urban construction, 50 gallons of recoverable rainfall are lost each year, while for each acre of land occupied by humans the water that could be destined for more than 3,000 families is lost. With the relentless urbanisation of every part of the Mexico City valley, water is becoming less and less a renewable resource and more and more a scarce commodity.

Long drain running

Although the excrement that I and millions of others dump each day into toilets throughout Mexico City takes an amazing voyage beneath the city streets, through 6,000 miles of pipes, 68 pump stations and across almost 100 miles of canals, tunnels, dikes and artificial lakes, it has an uncanny knack of finding its way back to me.

Public bathrooms have recently grown into an important service industry in Mexico City (charging up to the equivalent of an hour of minimum wage). Photograph: Kurt Hollander

The disposal of human sewage (known as aguas negras) has always been a major problem. Since the Spanish colony was first established here, canals and rivers have been used as dumping grounds for human faeces, with thousands of prisoners and indigenous workers forced to dredge the constantly clogged waterways. The fresh water lakes that irrigated the city's crops and provided drinking water also served as dumping grounds for humans, and this contaminated water (so toxic it was said to burn duck feathers) spread its stench and disease throughout the city. To deal with this situation, three huge, costly sewage works (the Western Interceptor in 1789, the Great Canal in 1900 and the Central Source in 1975) were built to funnel the aguas negras out of the city. As a result, a good chunk of the city's human sewage now rides rivers all the way out to the Gulf of Mexico or the Pacific Ocean. Most, however, remains much closer to home.

In 1971, the federal government selected the Mezquital valley in the state of Hidalgo, about 50 miles north of Mexico City, as the ideal destination for the majority of the capital's massive amount of human waste. In fact, though, towns in the region had already been receiving faecal matter from the capital ever since the first sewage pipe funnelled excrement outside of Mexico City in 1608. As the land in the Mezquital valley is arid and lacks its own water supply, raw sewage from Mexico City is used to irrigate almost 40,000 acres of cropland. The sewage sent to the area receives absolutely no treatment, even the most basic one of separating solids from liquids, and thus the valley, watered by the greatest concentration of aguas negras in all of Latin America, is commonly referred to as the world's largest outhouse.

Human sewage might help float the local economy but it does so at a price. In return for being able to use sewage as a source of water for crops, locals suffer the stench that emanates from the miasma, and hordes of flies, rats, and other vermin invade the towns in search of sustenance. Local farmers are prone to several acute and chronic health problems, especially skin and intestinal diseases caused by all sorts of especially nasty parasites, but they are not the only people infected. The vegetables grown in the valley (along with all the microorganisms residing within) are transported daily to Mexico City's markets and supermarkets and can wind up in my salad.

Much of Mexico City's raw sewage, however, never even leaves the city. During the dry season, excrement in the open-air sewers dries up and goes airborne, returning to the city with the first rainfall or as brown snowflakes. Due to all the leaky or burst pipes, aguas negras constantly escape from the sewage system and leech down into the earth beneath the city. This underground sea of sludge, however, especially during rainy season, has a way of surging up to the surface, flooding homes throughout the city and provoking health disasters (during the 2011 "great black flood", 60,000 inhabitants in a single neighborhood had their homes inundated by dark rivers).

Official figures state that more than one-third of all the water that now flows through Mexico City's water system leaks out of the underground pipes at a rate of 12,000 litres per second, a total loss of over 1bn litres a year. Given that the aguas negras are much more corrosive, who knows what amount of faeces leaks out of its pipes and filters down into water basin or into the pipes that provide drinking water.

A manhole cover in Mexico City – the tap water in the city leads to the highest rate of gastro infections in the world. Photograph: Kurt Hollander

The tap dance

WC Fields, the great comedian and unrepentant alcoholic, was once claimed to have said that he never drank water because fish copulate in it. In Mexico City, it's not the fish you have to worry about. Unlike tap water in major European and American cities, there is incredible biodiversity in a single drop of Mexico City tap water. The city ranks number one in the world when it comes to gastrointestinal infections (about 90% of adults in the city are infected with Helicobacter pylori) and its drinking water has been shown to be an ideal vehicle for the transmission of salmonella, dysentery and a host of other common diseases.

One recent study by researchers at the Universidad Nacional Autónoma de México analysed 100 samples of tap water in Mexico City and found 84 microorganisms of nine different species, all of which are usually present in human and animal waste. One bacteria, helicobacter pylori, associated with ulcers and gastric cancer, was found in all samples, while E coli, which causes diarrhoea and urinary tract infections, was also well represented. Viruses, including the Legionella virus of hepatitis A and rotavirus, which can lead to liver and respiratory disease, also showed up in the tap water tested.

As the water used for public swimming pools and parks is treated water (that is, recycled sewage), the quantity of microorganisms is much higher than in tap water. Although international health standards recommend keeping the limit under one parasite egg for every litre of treated sewage water, in Mexico the acceptable limit is five.

A woman rehydrates with some agua embotellada in Mexico City. Mexico is the second largest consumer of bottled water in the world. Photograph: Marco Ugarte/AP

Although few humans drink treated sewage water, most pets do (my cat seems to prefer toilet to tap water), and thus almost all are infected with parasites (and often pass them along to their owners). For instance, one gramme of dog faeces can contain up to 15,000 Cryptosporid eggs. Besides infecting humans, dogs and cats, the Cryptosporid parasite, one of the newer parasites on the scene, infects fish, birds, rats, deer, snakes, sheep, horses and pigs, and studies have found that about half of all cows raised for their milk are infested with Cryptosporid. Outbreaks of this parasite in Mexico City occur from contaminated water, contagion in hospitals and childcare centres, contact with infected animals or animal products, and from people who engage in oral or anal sex.

When humans get sick from an infectious illness, related health problems increase, especially heart disease. Secondary, chronic illnesses (meningitis, respiratory diseases, arthritis, birth defects, reproductive problems, cancer, hepatitis, and liver, kidney and heart problems) are often a legacy of gastrointestinal infections. Helicobacter bacteria can cause gastritis or colitis, which can in turn lead to ulcers and cancer, Salmonella can leave people with arthritis and colitis (as happened to me), while E coli can lead to kidney failure and hemorrhages. Some bacterial infections lead to thyroid immune dysfunction or neuronal paralysis, while viral infections have been shown to be involved in the onset of diabetes.

In addition to health problems associated with parasites in developing countries, Mexico City suffers many of the same problems as industrialised nations, including the contamination of the air, ground, food and water by toxic chemicals. Of the 4m tonnes of toxic waste generated in Mexico City each year, more than 95% is dumped directly into the city's sewer system. The chemical and petrochemical industries within the city generate 2.5m tonnes of hazardous waste, with only 15% treated in any way and the rest drained directly into the water supply. The most dangerous chemicals found in Mexico City water are nitrates, toxic metals, organic solvents, agricultural pesticides, herbicides and radioactive chemicals. Some of these chemicals can provoke acute and chronic toxicity while others can have harmful effects on human genes that lead to mutations and cancer. Floating within the city's water supply are also endocrine disruptor compounds, such as certain insecticides, hydrocarbons, polyaromatics, as well as pharmaceuticals and steroids that can disrupt the normal activity of human hormones, and can affect several inner organs and even reproductive organs (causing lower sperm count or fecundity). These aggressive chemicals commonly found in tap water aren't eliminated by saturated carbon or ozone filters or by boiling and thus are often present in tap water in buildings such as mine and even in the water distributed in plastic jugs.

In Mexico City, water is no longer innocuous but has instead become a tricky, potentially lethal substance. No one in Mexico City has ever drowned in a glass of water, but just by drinking water in the city many a life has been cut short.

Bottled safety?

Like all gringos, when I first arrived in Mexico City I was warned about drinking the water. Nonetheless, I regularly drank aguas de frutas in markets and on the streets and ate fruit ices made from water. Apart from several bouts of weird bowel movements, nothing really bad happened to me.

After getting salmonella and a subsequent outbreak of chronic, ulcerative colitis, however, water, the substance most present in my body and crucial for my survival, began to make me very nervous, fearing that even brushing my teeth, gargling or singing in the shower could do me in.

In the 1990s, following a cholera outbreak that killed more than 500 people, the Mexico City government increased the chlorine content in tap water as a safety measure. Besides leading to health problems (such as genetic mutations) that occur from consuming chlorine or as a result of the reaction between chlorine and faeces in the water pipes, the resulting unpleasant smell (much like swimming pool water) and taste made most people shy away from tap water.

City workers deliver a weekly water ration in drums and buckets at a low-income neighborhood in Mexico City.

Although water is a naturally occurring substance, most water drunk in Mexico City is now purchased and consumed from a plastic bottle. Mexico ranks second in the world in per capita consumption of bottled water, now the single most profitable product ever sold. In Mexico, bottled water is a multimillion dollar business, outselling soft drinks by 20%. Although multinational giants dominate the bottled water market, there are hundreds of local bottling firms, most of which are not licensed or regulated in any way, that compete for their market share.

Even though it costs thousands of times more than tap water, there is no assurance that the quality of water inside a plastic bottle is any better. Many brands claim to use electrolysis as a purification process, yet their bottled water is often merely filtered city tap water, with the toxic and parasitic ingredients intact. This is a common practice around the world, and not just among the illegal bottlers.

The quality of ice tends to be even worse, as the ice industry is even less supervised and regulated than the water industry. Besides the thousands of legal ice manufacturers, there are up to 6,000 unlicensed and unregulated companies in Mexico that make ice. Industrial ice, which represents 60% of all ice produced, is usually just frozen tap water.

Freezing does not kill parasites in water, but even if the water used is pure, the large blocks of industrial ice transported around the city in trucks, on customised bicycle pushcarts or dragged along the sidewalk by giant metal tongs pick up parasites on the way to the consumer. Although these blocks of ice are not made for human consumption, they are often chipped by ice picks and sold as flavored ices or used to chill drinks and food.

Due to pressure from the World Bank and other international institutions, water first began to be privatised in the 1980s with the sale of dams, the private control of the public water supply and the large-scale marketing of bottled water. In Mexico, water is auctioned off wholesale to the highest global bidder and multinational companies now lease or buy the land in which a water source is located and pay only a nominal fee to obtain unlimited access. Once they legally own the rights to water sources in Mexico, some multinational companies go to such extremes as to prohibit locals from collecting rainfall, claiming that this is their private property.

If, one day, the leaks in the water pipes were fixed and the city's water system repaired, if instead of dumping rain and river water out of the city it were collected to be used as drinking water, if people and corporations didn't dump their waste directly into rivers and lakes, the city might once again, as in the days of the Aztecs, have a naturally replenishing, self-sustaining, truly inexpensive supply of clean drinking water. As a result, many consumers within the city would save a substantial portion of their income, the government would save millions by not having to subsidise its supply and the ground water would be replenished.

With the huge profits being made from the privatisation of water in Mexico, however, this doesn't seem likely. Meanwhile, toxic substances and parasites transported around the city by different water sources continue to accumulate within my inner organs, paving the way for liver disease or cancer caused by dirty city water.

Kurt Hollander is a writer and photographer who has lived in Mexico City since 1989. This article is an adapted excerpt from his book, Several Ways To Die In Mexico City (Feral House)