Let's say nobody answers with what you're really looking for. This is really not what you're looking for, but it will work.

Construct a three-output manifold with an electrically controlled valve on each section. Add a variable valve to sections two and three. Set variable valve two to half flow and set variable valve three to one quarter flow. The outputs of these valves are combined in another manifold, resulting in a single pipe output.

A set of macros work this way:
All off gives you no water flow
Only 3 on gives you one quarter flow
Only 2 on gives you half flow
Both 2 and 3 on gives you three quarters flow
1 on gives you full flow (1 could instead be another variable valve set to one quarter so that full flow is 1 and 2 and 3 on)

Primitive? Right. It's a two bit controller (with all on added), after all. And how many steps of percentage do you need? "Percentage" implies a hundred values, so 128 values or seven valves plus the full on. That seems excessive.

Instead of the adjustable valves, you could insert smaller diameter pipe sections to constrict flow to one quarter and one half, respectively, but this is even tweakier than the multivalve approach.

As for the number of bits, I expect to see arguments. A true two-bit controller would have four outputs: zero, one quarter, one half, and three quarters. Zero is a meaningful value in digital counting, but with water flow, binary 11 is only 3/4 of full flow. Omitting full on is ridiculous.

And, of course, adjust to taste. I think if you add one more bit you're starting to get excessive. Maybe not.