Water.use Income Number.of.Children.below.5 Diorrheal.incidence P0U.use
1        100  12000                          0                   0       1
2        120  13000                          1                   0       1
3        130  13000                          2                   0       1
4         96  12000                          0                   1       0
5         95  13000                          1                   1       0
6         95  11000                          0                   1       1
7         98  12000                          1                   1       0
8         97  11000                          0                   1       0
9         92  10000                          1                   1       0
10       103  12000                          0                   0       1
11       105  12500                          1                   0       1
12       101  12000                          0                   0       1
13       100  12000                          1                   0       0
14        97  11000                          2                   1       0
15        99  11000                          1                   1       0
16       100  12000                          0                   0       1
17       101  13000                          0                   0       1

library(ltm)
biserial.cor(df1$Water.use, df1$Diorrheal.incidence)
#[1] 0.5547232