From bleach to disinfectant
Chlorine was identified as an element in the 1770s, and by the early 1800s chemists and industries were using chlorine compounds to bleach textiles and paper. Chlorine-based solutions were also used in the 1800s to deodorize rooms and treat wounds and hospital areas. Physicians such as Ignaz Semmelweis in Vienna in the 1840s asked staff to wash hands in a chlorinated solution, a practice linked to the history of antiseptic surgery. None of this was aimed at drinking water.
The idea of adding such compounds to a public water supply came only after bacteria were established as the cause of waterborne disease. By the 1880s and 1890s, researchers had shown in the laboratory that certain chemicals killed the organisms behind typhoid and cholera. Whether that could be done safely and cheaply at city scale was the open question.
Early trials
The first uses were improvised. In 1897, a typhoid outbreak in Maidstone, in Kent, England, led the bacteriologist Sims Woodhead to disinfect the town’s water mains with a bleaching compound as an emergency measure. It is often cited as one of the earliest uses of chlorine for a public water system, though it was a temporary response and not a permanent treatment. In the early 1900s, a Belgian water works at Middelkerke is generally credited with an early continuous application. England saw further uses after epidemics, such as in Lincoln in 1905, but the practice was not yet routine, and the evidence is clearest for the cases that were reported.
The best known and most influential trial took place in the United States. In 1908, Jersey City, New Jersey, began dosing the water from its Boonton Reservoir with a hypochlorite solution, under the direction of the physician John L. Leal, with engineering help from George Fuller. The decision was controversial. Some people thought it was dangerous to add a chemical to drinking water, and the city was taken to court. The court case is remembered for a judge’s decision to accept the evidence and allow the treatment to continue. The treatment worked, in the sense that bacteria counts fell and typhoid cases afterward declined, though other improvements were happening too. The point is widely treated as a turning point for water chlorination in North America.
Why it spread
Chlorination spread quickly for practical reasons.
- Low cost. It required only a chemical and a feeding device, not a great stretch of land for filter beds.
- Speed. A water works could start dosing in weeks, unlike large construction projects.
- Fit. It could be added to a system that already filtered water, or to one that did not.
- Effect. It killed the typhoid and cholera organisms that were the leading worries.
The chemical supply improved in the 1910s. At first, plants used bleaching powder, a solid that was dissolved and dosed. Later, liquid chlorine in steel cylinders became available, supplied by a growing industrial chemistry sector that could produce chlorine in bulk. Specialized feeding equipment was developed to measure doses accurately, a necessity since too little chlorine fails to disinfect and too much can affect taste. By the end of the 1910s, many large American cities had adopted it, and European and other cities followed over the next decades.
Most historians agree that chlorination, combined with filtration, played a major role in the fall of typhoid in cities. They also caution that milk safety, improved sewage disposal, and food handling occurred during the same years, so the chlorine share cannot be pinned down exactly. The role of safer milk is told in the history of milk pasteurization.
Other disinfectants
Chlorine was not the only option. Ozone, a form of oxygen, was used for drinking water at Nice, France, in the early 1900s and earlier in experimental plants in the Netherlands. It is effective but more costly to generate and leaves no lasting protection in pipes. Ultraviolet light was tested early and became widespread much later, as lamp technology improved. Chloramines, a combination of chlorine and ammonia, came into use in the twentieth century in some systems because they last longer in long pipe networks.
That last point matters: a residual amount of chlorine in the distribution system provides continuing protection against contamination after treatment. It is one of the reasons the method became a default.
Debates and later concerns
Chlorination was never free of argument. Early opponents objected to the idea of adding a chemical at all. Others complained about taste and smell. In the 1970s, researchers found that chlorine can react with natural organic matter in water to form by-products, such as trihalomethanes. This led regulators and water works to review their processes, adjust where in the plant chlorine is added, and in some cases use alternative disinfectants. The consensus among public health bodies has remained that the risk of waterborne infection from untreated water is far greater than the risk from these by-products, though it is reasonable to describe the issue as one of ongoing refinement.
Chlorine also does not do everything. It is less effective against certain hardy organisms, such as some parasites, which is a reason that filtration and other methods are still combined with it. This is why water works treat disinfection as one step in a sequence, as described in the broader history of sand filtration and sewer systems.
A lasting practice
By the middle of the twentieth century, chlorination was a routine feature of urban water supplies in much of the world. It remains in wide use today, the same basic principle as in Jersey City, applied with better monitoring and control.