from https://community.home-assistant.io/t/water-leakage-notification-blueprint/273031/10

moisture_alarm.yaml

blueprint:
  name: Moisture Sensor
  description: Perform action when moisture sensor turns wet
  domain: automation
  input:
    actions:
      name: Actions
      description: Notifications or similar to be run.
        {{ trigger.event.data.new_state.attributes.friendly_name }} will be the name of the
        sensor
      selector:
        action: {}
trigger:
  - event_data: {}
    event_type: state_changed
    platform: event
condition:
  - condition: template
    value_template: '{{ trigger.event.data.new_state.attributes.device_class == "moisture" }}'
  - condition: template
    value_template: '{{ trigger.event.data.new_state.state == "on" }}'
action:
- choose: []
  default: !input 'actions'
mode: single