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The presence of E. coli was variable between domestic greywater sources (Table 2) and geographic areas (Table 3). Median levels of E. coli ranged from 100 colony forming units (cfu)/100 ml for handwashing stations to >20,000 cfu/100 ml for greywater from washing vegetables and cleaning a home/kitchen. Greywater sources also exhibited variability in levels of total coliform, with median concentrations ranging from 9,100 to >20,000 cfu/100 ml. For greywater after cleaning a home/kitchen and washing vegetables, each sample contained >20,000 cfu/100 ml. Total coliform bacteria come from a variety of sources and will regrow in untreated water, which means they are not strongly indicative of fecal contamination in greywater, unlike E. coli (WHO 2011). The WHO guideline for using greywater for the unrestricted irrigation of root crops that will be consumed without being cooked is an arithmetic mean of 1,000 E. coli colonies per 100 ml (WHO 2006). The most stringent WHO guideline is applied to root crops that will be eaten raw, as root crops would come into direct contact with greywater during irrigation and have a relatively higher risk of disease transmission, as opposed to other crop types, such as tall-growing fruit trees. Twenty-four of the 47 greywater samples tested (51%) had less than the WHO guideline of 1,000 E. coli cfu/100 ml. The median E. coli concentration of five out of eight (63%) greywater category sources tested was less than 1,000 cfu/100 ml. One-sample sign tests were used to determine whether the median E. coli concentration of greywater from each source differed significantly from the WHO guideline (WHO 2006). It was found that each source except cleaning a home/kitchen (>20,000 cfu/100 ml, N = 7, p = 0.016) did not differ significantly from the WHO guideline (WHO 2006). The median E. coli concentration of greywater samples was less than the WHO guideline for unrestricted irrigation of root crops for only three geographic areas (Tanks 2, 3, and 6). One-sample sign tests showed that the median E. coli concentration of each geographic area was statistically equivalent to 1,000 cfu/100 ml. Chi-squared tests were used to determine that the geographic area of a sample was not strongly related to the amount of E. coli or total coliform (X2(N = 47) = 99.505, p = 0.356, and X2(N = 47) = 70.775, p = 0.161, respectively).

Table 2

E. coli and total coliform test results by domestic greywater source

Greywater sourceE. coli (cfu/100 ml)
Total coliform (cfu/100 ml)
N
MaximumMeanMedianMinimumMaximumMeanMedianMinimum
Bathing 8,800 3,300 400 >20,000a 10,600 9,100 1,600 
Cleaning home/kitchen >20,000a 16,200 >20,000a 2,500 >20,000a >20,000a >20,000a >20,000a 
Cleaning water collection container >20,000a 6,900 700 >20,000a 17,100 >20,000a 2,300 
Handwashing station 13,600 2,900 100 >20,000a 17,400 >20,000a 10,800 
Runoff from tap apron 6,500 6,500 6,500 6,500 11,400 11,400 11,400 11,400 
Washing clothes >20,000a 3,400 600 >20,000a 18,000 >20,000a 6,800 14 
Washing plates >20,000a 5,900 600 >20,000a 14,800 >20,000a 1,300 
Washing vegetables >20,000a >20,000a >20,000a >20,000a >20,000a >20,000a >20,000a >20,000a 
WHO guideline for unrestricted irrigationb – ≤1,000 – – – – – –  
Greywater sourceE. coli (cfu/100 ml)
Total coliform (cfu/100 ml)
N
MaximumMeanMedianMinimumMaximumMeanMedianMinimum
Bathing 8,800 3,300 400 >20,000a 10,600 9,100 1,600 
Cleaning home/kitchen >20,000a 16,200 >20,000a 2,500 >20,000a >20,000a >20,000a >20,000a 
Cleaning water collection container >20,000a 6,900 700 >20,000a 17,100 >20,000a 2,300 
Handwashing station 13,600 2,900 100 >20,000a 17,400 >20,000a 10,800 
Runoff from tap apron 6,500 6,500 6,500 6,500 11,400 11,400 11,400 11,400 
Washing clothes >20,000a 3,400 600 >20,000a 18,000 >20,000a 6,800 14 
Washing plates >20,000a 5,900 600 >20,000a 14,800 >20,000a 1,300 
Washing vegetables >20,000a >20,000a >20,000a >20,000a >20,000a >20,000a >20,000a >20,000a 
WHO guideline for unrestricted irrigationb – ≤1,000 – – – – – –  

– No established value.

aResult was too numerous to count, upper limit of detection for this method is reported.

bWorld Health Organization (2006).

Table 3

E. coli and total coliform test results by tank number

Tank No.E. coli (cfu/100 ml)
Total coliform (cfu/100 ml)
N
MaximumMeanMedianMinimumMaximumMeanMedianMinimum
>20,000a 7,100 2,500 >20,000a 16,300 >20,000a 2,500 
>20,000a 6,300 400 >20,000a 12,700 >20,000a 1,300 
>20,000a 9,000 600 >20,000a 18,500 >20,000a 6,800 
>20,000a 10,100 10,700 >20,000a 18,200 >20,000a 10,800 
>20,000a 5,500 1,100 >20,000a 18,100 >20,000a 2,300 15 
400 300 300 200 >20,000a 15,600 15,600 11,200 
WHO guideline for unrestricted irrigationb – ≤1,000 – – – – – –  
Tank No.E. coli (cfu/100 ml)
Total coliform (cfu/100 ml)
N
MaximumMeanMedianMinimumMaximumMeanMedianMinimum
>20,000a 7,100 2,500 >20,000a 16,300 >20,000a 2,500 
>20,000a 6,300 400 >20,000a 12,700 >20,000a 1,300 
>20,000a 9,000 600 >20,000a 18,500 >20,000a 6,800 
>20,000a 10,100 10,700 >20,000a 18,200 >20,000a 10,800 
>20,000a 5,500 1,100 >20,000a 18,100 >20,000a 2,300 15 
400 300 300 200 >20,000a 15,600 15,600 11,200 
WHO guideline for unrestricted irrigationb – ≤1,000 – – – – – –  

– No established value.

aResult was too numerous to count, upper limit of detection for this method is reported.

bWorld Health Organization (2006).

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