Click on the chart and use the left and right arrow keys to walk the steps. Each step announces its contribution — what the bar's height actually is — alongside the running total it produced, which is where the bar sits. A bar chart would conflate the two, and answering only one of them answers half the question a waterfall is drawn for. Press B for braille, T for text descriptions, and S to toggle sonification.
A row marked isTotal: true restates the running total rather
than changing it: it sits on the baseline and is announced as a total. The
first step is read as one too, whether or not it says so — nothing is
carried into it.