If you need more precision, and if the pill ingredient can allow it 

- dissolve the pill in 100 ml (0.1 litre) of clean water
- in a measuring flask / bottle

then when you need to drink some of it, it will be easy to use exactly only the right proportion.

[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/wdreq.jpg