diff --git a/homeassistant/components/watttime/diagnostics.py b/homeassistant/components/watttime/diagnostics.py
new file mode 100644
index 00000000000..080c7c37b07
--- /dev/null
+++ b/homeassistant/components/watttime/diagnostics.py
@@ -0,0 +1,42 @@
+"""Diagnostics support for WattTime."""
+from __future__ import annotations
+
+from typing import Any
+
+from homeassistant.components.diagnostics import async_redact_data
+from homeassistant.config_entries import ConfigEntry
+from homeassistant.const import (
+    CONF_LATITUDE,
+    CONF_LONGITUDE,
+    CONF_PASSWORD,
+    CONF_USERNAME,
+)
+from homeassistant.core import HomeAssistant
+from homeassistant.helpers.update_coordinator import DataUpdateCoordinator
+
+from .const import DOMAIN
+
+TO_REDACT = {
+    CONF_LATITUDE,
+    CONF_LONGITUDE,
+    CONF_PASSWORD,
+    CONF_USERNAME,
+}
+
+
+async def async_get_config_entry_diagnostics(
+    hass: HomeAssistant, entry: ConfigEntry
+) -> dict[str, Any]:
+    """Return diagnostics for a config entry."""
+    coordinator: DataUpdateCoordinator = hass.data[DOMAIN][entry.entry_id]
+
+    return async_redact_data(
+        {
+            "entry": {
+                "data": dict(entry.data),
+                "options": dict(entry.options),
+            },
+            "data": coordinator.data,
+        },
+        TO_REDACT,
+    )
diff --git a/tests/components/watttime/conftest.py b/tests/components/watttime/conftest.py
index 84d8704eb1e..6483778c153 100644
--- a/tests/components/watttime/conftest.py
+++ b/tests/components/watttime/conftest.py
@@ -8,7 +8,11 @@ from homeassistant.components.watttime.config_flow import (
     CONF_LOCATION_TYPE,
     LOCATION_TYPE_COORDINATES,
 )
-from homeassistant.components.watttime.const import DOMAIN
+from homeassistant.components.watttime.const import (
+    CONF_BALANCING_AUTHORITY,
+    CONF_BALANCING_AUTHORITY_ABBREV,
+    DOMAIN,
+)
 from homeassistant.const import (
     CONF_LATITUDE,
     CONF_LONGITUDE,
@@ -21,11 +25,13 @@ from tests.common import MockConfigEntry, load_fixture
 
 
 @pytest.fixture(name="client")
-def client_fixture(get_grid_region):
+def client_fixture(get_grid_region, data_realtime_emissions):
     """Define an aiowatttime client."""
     client = Mock()
     client.emissions.async_get_grid_region = get_grid_region
-    client.emissions.async_get_realtime_emissions = AsyncMock()
+    client.emissions.async_get_realtime_emissions = AsyncMock(
+        return_value=data_realtime_emissions
+    )
     return client
 
 
@@ -61,7 +67,12 @@ def config_entry_fixture(hass, config_auth, config_coordinates, unique_id):
     entry = MockConfigEntry(
         domain=DOMAIN,
         unique_id=unique_id,
-        data={**config_auth, **config_coordinates},
+        data={
+            **config_auth,
+            **config_coordinates,
+            CONF_BALANCING_AUTHORITY: "PJM New Jersey",
+            CONF_BALANCING_AUTHORITY_ABBREV: "PJM_NJ",
+        },
     )
     entry.add_to_hass(hass)
     return entry
@@ -73,6 +84,12 @@ def data_grid_region_fixture():
     return json.loads(load_fixture("grid_region_data.json", "watttime"))
 
 
+@pytest.fixture(name="data_realtime_emissions", scope="session")
+def data_realtime_emissions_fixture():
+    """Define realtime emissions data."""
+    return json.loads(load_fixture("realtime_emissions_data.json", "watttime"))
+
+
 @pytest.fixture(name="get_grid_region")
 def get_grid_region_fixture(data_grid_region):
     """Define an aiowatttime method to get grid region data."""
diff --git a/tests/components/watttime/fixtures/realtime_emissions_data.json b/tests/components/watttime/fixtures/realtime_emissions_data.json
new file mode 100644
index 00000000000..ee5d0ae2833
--- /dev/null
+++ b/tests/components/watttime/fixtures/realtime_emissions_data.json
@@ -0,0 +1,8 @@
+{
+    "freq": "300",
+    "ba": "CAISO_NORTH",
+    "percent": "53",
+    "moer": "850.743982",
+    "point_time": "2019-01-29T14:55:00.00Z"
+}
+
diff --git a/tests/components/watttime/test_config_flow.py b/tests/components/watttime/test_config_flow.py
index ddbe4ebff4a..514376d58a5 100644
--- a/tests/components/watttime/test_config_flow.py
+++ b/tests/components/watttime/test_config_flow.py
@@ -159,8 +159,6 @@ async def test_step_reauth(
             data={
                 **config_auth,
                 **config_coordinates,
-                CONF_BALANCING_AUTHORITY: "Authority 1",
-                CONF_BALANCING_AUTHORITY_ABBREV: "AUTH_1",
             },
         )
         result = await hass.config_entries.flow.async_configure(
diff --git a/tests/components/watttime/test_diagnostics.py b/tests/components/watttime/test_diagnostics.py
new file mode 100644
index 00000000000..0d8d87203bb
--- /dev/null
+++ b/tests/components/watttime/test_diagnostics.py
@@ -0,0 +1,28 @@
+"""Test WattTime diagnostics."""
+from homeassistant.components.diagnostics import REDACTED
+
+from tests.components.diagnostics import get_diagnostics_for_config_entry
+
+
+async def test_entry_diagnostics(hass, config_entry, hass_client, setup_watttime):
+    """Test config entry diagnostics."""
+    assert await get_diagnostics_for_config_entry(hass, hass_client, config_entry) == {
+        "entry": {
+            "data": {
+                "username": REDACTED,
+                "password": REDACTED,
+                "latitude": REDACTED,
+                "longitude": REDACTED,
+                "balancing_authority": "PJM New Jersey",
+                "balancing_authority_abbreviation": "PJM_NJ",
+            },
+            "options": {},
+        },
+        "data": {
+            "freq": "300",
+            "ba": "CAISO_NORTH",
+            "percent": "53",
+            "moer": "850.743982",
+            "point_time": "2019-01-29T14:55:00.00Z",
+        },
+    }