Use 'workable' for ideas or methods that can realistically be implemented or used. He devised a workable method for recycling the waste.
Pro Tip 2/3
Effectiveness Implied
'Workable' implies that something is not only possible but also effective and efficient in practice. We need a workable approach that meets all our objectives.
Pro Tip 3/3
Not Ideal
A 'workable' solution may not be perfect but it's good enough to solve a problem temporarily or under certain conditions. It's not the best option, but it's a workable compromise for now.