Variable type of sensor

I’m building a water sensor for my well. The POC nearly complete, and I get the measurements into HA as well (almost a dad joke).
The historical data however is presented as a colored bar instead of a line graph. How do I change that?

- platform: rest
  scan_interval: 300
  resource: !secret waterwell_url
  name: WaterWell_level
  value_template: "{{ value_json[0]['data']['Water'] | int * -1 }}"


Add a unit of measurement.

Thanks @tom_l !!
it really was that simple.

unit_of_measurement: cm