Drinking filtered tap water instead of bottled water would help the most with the problem of plastic waste and energy consumption associated with single-use plastic water bottles. This action significantly reduces the demand for bottled water production, thus decreasing plastic waste and the energy required for manufacturing and transporting those bottles.
While reusing a plastic water bottle at least twice is better than single-use, it still doesn't address the root of the problem, which is the production and disposal of plastic bottles. Therefore, choosing filtered tap water is the more effective action in helping to reduce plastic waste.