People in London in the mid-nineteenth century greatly feared cholera. At this time doctors ........... (believe) that cholera ......... (circulate) through the air, and .......... (not realize) that all the time raw sewage ......... (enter) water supply, and that the disease ........ (spread) through the domestic water system. Although in the 17th and 18th centuries London ....... (possess) a water supply system and a sewage system which were the changing situation. Broken water pipes and sewage pipes often ...... (flow) into one another, and most sewage ......... (end up) in the River Thames, which was the main source of drinking water for thousands. Between 1831 and 1867 a series of severe outbreaks ......... (occur). In the outbreak of 1848-49, there were over 30000 cases of the disease in London, and 15000 people .......... (die). By the mid 1860s the situation ......... (improve) mainly because by then engineers ........ (work on) the construction of a completely new sewage system, which they ......... (complete) in 1875, and which is still in use today.

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