1. Water without any additives, flavoring, or carbonation; tap water or distilled water in its simplest form
I prefer to drink plain water instead of sugary sodas.
Prefiro beber água pura em vez de refrigerantes açucarados.
2. Unflavored drinking water, as opposed to bottled, mineral, or flavored water
The doctor recommended drinking plain water throughout the day.
O médico recomendou beber água pura durante todo o dia.