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THE FILTERED WATER,
An inspection of the results given by the 129 samples of filtered water is in some respects disappointing.
No. 6 Bed filtering at 500 yards gallons was taken as the type and was therefore the most thoroughly tested. It required seven or more days after the commencement of this filter before it became effective; it then remained in working order till the 56th day when it was discarded by the Water Authority
Even at the best time of filtration the results are poor compared with what can be done at Home,
All the filters tested showed inefficency for the first week or more after their
commencement.
Coli may be got in even smaller quantities in the filtered water than in the unfiltered water when a bed is first started, apparently obtaining this increase from the sand of the filter, which had been previously used.
It is therefore undesirable to change more than one bed at a time otherwise the total filtered water for a week or so will be practically unfiltered.
As regards rates of filtration, 400-500 yards gallons appears to give as good a filtrate as 250-400 does; there is, however, no reason to believe that a rate of 700-800 yards gallons as is sometimes used (see Filtration Table for 1910) would be effective.
That the filtration is not as effective as obtains at Home seems to be another reason in favour of satisfactory preliminary storage of the water.
The other filter beds examined give probably a rather unduly unfavourable picture of the filtration as they were examined chiefly early after their commencement, when they were not really effective.
The following diagrams give a rough idea of the filtration from the point of view of the Coli Group. They can only be taken as approximate as all forms of Laotose fermenters are included and so the lines have by no means always an equal value. As far as they go however they give a general idea of how a filter bed starts.
OTHER PUBLIC WATER SUPPLIES IN HONGKONG.
Some forty-two samples of Filtered and Unfiltered Water taken from other sources of Water Supply in the Colony have also been examined since the beginning of this year.
Only a few of those samples gave results requring notice of which the chief are as follows:-
KOWLOON WATER.
Filtered water examined on four occasions: the total Colonies in one c.c. Agar varied from 10 to 25 giving an average of 17.5 per c.c. and the Coli Group was absent up to 50 c.c.
In the unfiltered water, the Coli Group varied from negative up to 20 c.c. down to present in 1 c.c.
On the whole, the Kowloon water gives very good Bacteriological results, better than any other water supply in the Colony.
TYTAM WATER,
Filtered.-Total Colonies on agar in 1 cc. varied from 10 to 40 on 7 occasions and 100 on one occasion and the Coli Group varied between present in 10 c.c. to absent in 20 c.c.; eight samples tested.
Unfiltered. The total Colonies on Agar in 1 c.c. varied from 60 to 320 on 13 occasions it was examined; the Coli Group was present in 10 c.c on 2 occasions, in 5 c.c. on 3 occasions, and during the month of May in 1 c.c.
Generally speaking this water supply occupies an intermediate position between the Kowloon and the Pokfulum Waters.
*Not Printed.