"Wretched houses with broken windows patched with rags and paper; every room let out to a different family, and in many instances to two or even three – fruit and ‘sweetstuff’ manufacturers in the cellars, barbers and red-herring vendors in the front parlours, cobblers in the back; a bird-fancier in the first floor, three families on the second, starvation in the attics, Irishmen in the passage, a ‘musician’ in the front kitchen, a charwoman and five hungry children in the back one – filth everywhere – a gutter before the houses, and a drain behind – clothes drying, and slops emptying from the windows; ... men and women, in every variety of scanty and dirty apparel, lounging, scolding, drinking, smoking, squabbling, fighting, and swearing."
Charles Dickens, Sketches by Boz, 1839, on St Giles Rookery
Calling the slums of Victorian London a dirty place is like saying eating forty Twinkies a day is bad for you. The above quotation from Mr. Dickens is indicative of the type of place most of the poorest denizens of the city lived in. We're talking conditions roughly equivalent to many Third World countries, but existing in the center of the most powerful country in the world at the time.
The poor lived in brownstone tenements and rickety shacks, some next to the Thames, which was a stinking cesspool of pollution that smelled worse than a decaying corpse when the summer heat got too bad. It didn't help that the mills and factories turning London into a capital of Industry and Progress, places that many of these poor worked, were the causes of the vast amounts of filth poured into the river day in and day out.
Sanitation might as well have been nonexistent in these areas. Hector Gavin wrote a set of "Sanitary Ramblings" focused on Bethnal Green (an area in the contemporary London borough of Tower Hamlets) in 1848, and revealed that the section had "thirty-three miles of streets and 100 miles of byeways, not counting the length of courts and alleys, which require drainage." Guess how many miles of sewer this 759-acre area had.
Less than seven and three-quarters.
Gavin goes on to explain that the main street through the district had no sewer at all for 1,600 yards of its length, and a mile and a half of the sewers Bethnal Green did have also served the areas of London to the north and south. And none of the sewers connected directly to any of the houses. Because of this, repeated outbreaks of diseases like cholera, typhus, influenza and scarlatina were commonplace.
So common were these outbreaks that Henry Mayhew in 1849 christened the south shore of the Thames with the name "Pestilensia." These same diseases hit the same areas of the city every year, with the only change being the end of the street that the disease started on.
These slums were the basis for both the Lowtown and Quayside districts of Callarion -- the city CALLARION AT NIGHT takes place in -- without getting into a lot of the gritty detail that the social critics of Victorian London did. Because while it creates realism, a lot of the info is extraneous to the story I'm trying to tell.