How much positive and negative charge is there in a cup of water?

Suppose the cup contains 250 cc of water.
Mass of 250 cm³ of water = 250 g
Molecular weight of water = 18 g
No. of molecules in 18 g of water = 6.023 X 10²³
No. of molecules in 250 g of water = $\frac{6.023 X {10}^{23} X 250}{18}$
As each molecule of water contains 10 electrons, therefore, total no. of electrons, 
$$\begin{gathered} n = \frac{10 X 6.023 X {10}^{23} X 250}{18} = 8.365 X {10}^{25} \\ As q = ne \\ q = 8.365 X {10}^{25} X 1.6 X {10}^{-19} C \\ = 1.338 X {10}^7 C \end{gathered}$$