Colourful maps and sketches, and rare views inside Hong Kong’s early tenement housing are bonuses in Mr Chadwick’s report on ‘the Sanitary Condition of Hong Kong’. We’ll take a look at all of the above, plus the old night-soil collections and the 19th-century revolution in understanding disease, in Gwulo’s latest YouTube video.
Comments
Water analyis
Thank you, David, for this interesting presentation. When you talked about water quality, you said that bacteriological analyses would have given a better insight compared to chemical analysis. This is, of course, correct, but these analyses were difficult and possibly not available in Hong Kong at the time when the report was written. Additionally, you mentioned the still widely accepted "Miasma Theory". In the analysis report you presented, "Smell" is the first column after origin and date. As you said, many people at that time still believed that diseases came from bad air (Malaria originated from the medieval Italian mala aria which simply means bad air).
However, some chemical parameters also give information about the water quality. Contamination of water results either from geogenic and/or anthropogenic sources. Geogenic (as the name indicates) contamination comes from the rocks underground where the wells are drilled into. On Hong Kong Island, the most abundant rock is granite, which will not leach a lot into groundwater. An indicator of that is chloride, and it is mostly present only in low concentrations.
Water pollution in Hong Kong, therefore, mainly comes from human activities. I guess we can exclude animals (cattle) in this context. Although "night soil" was collected, certainly a lot of human excrement was discarded "behind the next bush". This leached into the groundwater and was found in the wells. A (today) commonly used parameter for that is phosphate. Also, free ammonia indicates human activities.
No values are given for phosphate. But I think "heavy and very heavy traces" indicate poor water quality. It works better for ammonia where we have analytical results. Values are given in ppm which is approximately the same concentration as mg/l. The EU limit value for groundwater is 0,5 mg/l. Water with concentrations above is usually not regarded as a suitable source of human drinking water.
So, even without bacteriological investigation, the chemical analysis revealed a good insight into water quality, even with regard to human health risks.
One last remark: Even the "Miasma believers" will feel affirmed. Example:
No 5 well at Hollywell Road
Smell - distinct
phosphate - very heavy traces
free ammonia - 1,72 ppm
This, of course, does not work in every case:
No 11 well in Yu Yam Lane
Smell - faint
phosphate - heavy traces
free ammonia - 8.6 ppm