Drinking water has two sources. It can come from surface water, such as reservoirs or rivers. Or it can come from groundwater where it either naturally surfaces in a spring or where it must be pumped to the surface from a well. Where does your drinking water come from?

82% of drinking water supplies in Ireland are sourced from surface water (rivers and lakes) and 18% comes from groundwater - it depends where you live (quick g00gle search should answer you question)

when [oh-] is 10-5  m, and [h3o+] is 10-9  m, the poh is 5 and ph is 9. again in both cases the sum of ph and poh is 14. however, the hydrogen ion concentration is not always going to be equal to exactly 1 x 10 raised to a negative number. for example, we skipped over the value of 2.0 x 10-7.