Meanings of enough useable in English

Currently, the dam levels show only enough useable water to last until March next year.

With Cape Town currently only having enough useable water to last until March 2018, things are getting desperate for the city and its residents.

With the latest reports from the city of Cape Town stating that there is currently enough useable water to last until March of next year.

New Aer Corps trainee pilots could take up to five years to earn their wings because the force does not have enough useable training aircraf(...)