How to plot the data difference from the start of chart time

I have several data streams that increment over time, (water meter, rain gauge, power consumed) and want to show a cummulative chart where the leftmost value is zero.
So, in my rainfall chart for “This Year”, I want to show 0 for 1-Jan and the total accumulated rainfall through the year. If I show the rainfall chart for “Today” I want to chart the total rainfall so far today.

I found a solution here.
Create daily graph starting at zero (0)

Thanks to @coyote