When and how to introduce water to LO

Hi mummies, my LO is turning 5mo and am thinking can I start to introduce sips of water as she's been coughing for more than 2wk already and there is no medicine for baby less than 6mo. I have a straw spout from hegen and all rounder crown, wondering which one I should use to introduce LO to water? I saw online many people recommended Richell straw cup but since I have hegen accessories I hope not to spend extra money.