Ever wondered what those giant concrete cylinders lined up along Michigan Avenue are? Well, if you lived in D.C. at the turn of the twentieth century, they  might have saved your life.  

Those  eye-catching  cylinders are part of the now-defunct McMillan Sand Filtration Plant, built in 1905. It was the first system the District had in place to purify its water supply.  Using  the slow sand filtration method,  raw  water  from the McMillan reservoir trickled through layers of sand, gravel, and stones until it was clean.  The cylinders stored fresh sand to replace the top layer when it got too dirty from collecting pollutants.  Beneath the surface level of the plant, water flowed through the “Cave of the Thousand Devils” (an expansive  subterranean  chamber  so named by its  construction workers), and  into the city’s water mains, free of impurities.^[1] 

What kind of impurities? Beginning in the 1890s, typhoid was all over the headlines of Washington’s major newspapers. As new cases were reported  daily, stories like “Epidemic of Typhoid” and “All Records Broken: Typhoid Fever Makes Rapid Gain” filled  the front pages seemingly every week.^[2] In 1900, Professor H.D. Geddings, acting director of the Marine Hospital Service’s hygienic laboratory  warned  the  public:  

Some method should at once be adopted for the purification of the District water supply. Not only is typhoid fever epidemic practically, but the city of Washington enjoys the unsavory reputation of having one of the largest death rates from typhoid in the United States, and typhoid being a strictly preventable disease, this state of affairs is a reproach and must soon seriously militate against the prosperity and advancement of the city.”^[3]

As Geddings suggested, the cause of this health emergency was D.C.’s drinking water.  

For decades, the city's water had flowed through the  Washington Aqueduct,  which dated to 1853 and was still  very much a work in progress. It started with a  diversion dam spanning the Potomac River, just above Great Falls. From there, water passed through the  Dalecarlia  Reservoir and the Georgetown Reservoir. Once the McMillan Reservoir was built in 1902, all that raw Potomac water settled  there  before going  straight to people’s faucets.^[4]

The result could be unpleasant or, in the worst cases, deadly. The Washington Post  painted  a clear picture of the murky water coming out of the tap at the turn of the century: 

Up to this time the water supply of the city has been turbid during one third of the year, at times so much so as to render the water absolutely unfit for either drinking, laundry or bathing purposes.”^[5] 

D.C. authorities blamed  the problem on  towns upriver, as far away as Cumberland,  Maryland, dumping refuse into the Potomac watershed. The War Department (in charge of the District water supply since a time before any D.C. government existed) insisted that the Potomac  River was in fact much cleaner than those in other cities,^[6] even though  bacteria from human fecal matter was found in  the  river in  large  quantities.^[7]

Typhoid death tolls kept rising, and the city was faced with a crisis. In 1901, the Senate District Committee, headed by Senator  James  McMillan of Michigan (namesake of the McMillan Plan to develop Washington’s monumental core and remake the National Mall) met at the Waldorf-Astoria hotel in New York City to listen to experts and resolve the problem.  Over the course of the  hearing, it became clear that widescale water filtration would be necessary.^[8] 

  But until a plant could be built, all Washingtonians could do was boil their water and bide their time, as The Washington Post lamented in 1900:  

From present indications there is no relief for the city inside of from three to four years. A filtration plant, the one thing that will prevent the wholesale contraction of typhoid, is to be constructed in the vicinity of the Soldiers’ Home. The foundations are now being built, but it is estimated that it will not be completed before the later part of 1903 or the early part of 1904.” ^[9] 

D.C.  Commissioner Henry MacFarland  found a way for the  plant to ease into operation,  suggesting  that  each filter bed  be put into  service as soon as it was completed. With progressively more and more clean water entering the water supply as time went on, the dirty water would be diluted. MacFarland offered an explanation that any barfly could appreciate:

It is on the same principle that the addition of water to whisky reduces the harmful effect of the liquor in just the proportion of its dilution. It is obvious that a man swallowing a drink of half whisky and half water would imbibe exactly 50 per cent of the alcohol taken by the man who swallows his whisky ‘straight.’”^[13]