Sessional_Paper_1911 — Page 211

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(II) THE TOTAL Water.

These four intakes with others go to make up the total Pokfulum unfiltered

water.

This total unfiltered water was examined on 130 occasions and in 23 of these examinations the Group +(S-D+) was found 17.6%. This result is very similar to that given by the total intakes where 119 samples gave 21 positive or 17.6%.

In 16 out of the 23 cases in which the Group + (S-D+) was found, organ- isms giving the reactions of B. Coli Communis were isolated; in the remaining seven cases, the organisms were not further tested.

As regards the lowest amount of the samples in which these organisms were found, it was as follows:-

ro cc., on 2 occasions.

1 cc., on

8

17

2 cc., on

5 cc., on 3

10 cc., on 3

23

19

19

RESULTS OBTAINED FROM No. 6 FILTER BED.

Area of bed 330 sq. yards. Fine sand 2′ 3" deep overlying fine and coarse stone, The Bed was built on the ridge and furrow system, and is fitted with a regulating valve whereby the rate of filtering can be adjusted to suit requirements.

The sand was last cleansed on Wednesday, 2nd November, and the Bed was recharged with filtered water.

The rate of filtration was maintained at 500 gallons per sq. yd. per day throughout.

The Bed received the total mixed unfiltered water from the Catchment area.

The first sample was taken on the 5th November and the last on the 29th December, 1910, after which the Bed was discarded by the Water Authority.

In all 45 samples of filtered water were examined.

The results are recorded exactly as for the total unfiltered Pokfulum Water and the same explanation of signs applies equally here.

Samples 1 to 38 inclusive had lec., 2cc. and 5cc. added to Lactose Neutral Red Bile Salt Peptone water and lcc., 2cc., 5cc., 10cc., 20cc., and 50cc. added to Glucose Neutral Red Bile Salt Peptone water. .

Samples 39 to 45 had 1cc., 2cc., 5cc., 10cc., 20cc. and 50cc. added to Lactose Neutral Red Bile Salt Peptone water and lec., 2cc, and 5cc. to Glucose Neutral Red Bile Salt Peptone water.

In all other respects as regards incubation, plating out and determining the lowest amount of the sample to contain numbers of the Coli Group, the method is exactly that used for the unfiltered water already recorded.