Can this IBC be used for rainwater harvesting?

Yes. In fact, not only can it be used, but a reconditioned IBC is one of the most cost-effective ways of storing rainwater. And with a few additions it can be even more useful: Raise it: A steel IBC stand allows for a gravity-fed flow through a hose or tap (for this we would recommend the Hozelock adaptor or gravity hose kit). Keep light out: A translucent bottle is useful for a visible water line, but because it also lets light through, it can encourage algae growth. An outdoor IBC cover or black bottle helps with this. Filter the inlet: A 150mm lid with a mesh filter keeps leaves and debris out