diff --git a/app/integrations/expose.py b/app/integrations/expose.py
index 2ab71cf..1a4e70c 100644
--- a/app/integrations/expose.py
+++ b/app/integrations/expose.py
@@ -1028,7 +1028,7 @@ def _m8_energy_provider(session: Session) -> list[ExposableEntity]:
         elif meter.commodity == "heating":
             unit, device_class = "GJ", "energy"
         else:
-            unit, device_class = "m³", "volume"
+            unit, device_class = "m³", "water"
         for suffix, getter in (
             ("total", _meter_total_getter(binding.id, source.id, channel.id)),
             ("today", _meter_today_getter(binding.id, source.id, channel.id)),
diff --git a/docs/design/m8-warmtelink-energy.md b/docs/design/m8-warmtelink-energy.md
index de8b083..b9ad1f0 100644
--- a/docs/design/m8-warmtelink-energy.md
+++ b/docs/design/m8-warmtelink-energy.md
@@ -1214,6 +1214,12 @@ M8 收尾的前置条件。agent 不得执行、记录为已执行，或以 mock
 
 ## 14. Post-M8 lifecycle repair（M8-R08～R10）
 
+### M8-R16 — HA Water Energy Discovery metadata
+
+active `hot_water` Meter 的 total/today MQTT Discovery metadata 从通用 `volume` 修正为 Home
+Assistant Energy Water 所要求的 `water`；保留 `m³` 与 `total_increasing`。区域供暖继续使用合法的
+`energy + GJ` 组合，thermal EUR 成本实体以及既有 key、identity、unique_id 和 topic 均不变。
+
 ### M8-R15 — HA Discovery identity/topic repair
 
 修复 HA 将多值 `device.identifiers` 任一匹配合并的风险：Source、Meter、Modbus 与成本 epoch 均使用单一完整 namespaced identifier，内部 MQTT identity 独立保存。thermal 的既有点号 identity/key 保持兼容，node/object topic segment 单独规范化；仅对 v1.6.1 实际发布过的 dot topic 做可重试、成功后抑制的精确 retained cleanup。新增默认关闭的 `Thermal Hot Water Total/Today`，金额为 `hot_water_heating + hot_water`，不含 `hot_water_tax`。
diff --git a/tests/test_energy_expose.py b/tests/test_energy_expose.py
index 9021bf3..a610021 100644
--- a/tests/test_energy_expose.py
+++ b/tests/test_energy_expose.py
@@ -2788,7 +2788,11 @@ def test_m8_catalog_has_source_meter_and_thermal_entities_disabled(energy_db) ->
     assert entries[f"meter.{heating.uuid}.total"].entity.unit == "GJ"
     assert entries[f"meter.{heating.uuid}.total"].entity.device_class == "energy"
     assert entries[f"meter.{water.uuid}.total"].entity.unit == "m³"
-    assert entries[f"meter.{water.uuid}.total"].entity.device_class == "volume"
+    for suffix in ("total", "today"):
+        water_entity = entries[f"meter.{water.uuid}.{suffix}"].entity
+        assert water_entity.device_class == "water"
+        assert water_entity.unit == "m³"
+        assert water_entity.state_class == "total_increasing"
     assert entries[f"meter.{electricity.uuid}.total"].entity.unit == "kWh"
     assert entries[f"meter.{electricity.uuid}.total"].entity.device_class == "energy"
     assert entries[f"meter.{electricity.uuid}.today"].entity.state_class == "total_increasing"
@@ -2812,6 +2816,31 @@ def test_m8_catalog_has_source_meter_and_thermal_entities_disabled(energy_db) ->
     assert all(entry.entity.unit == "EUR" and entry.entity.device_class == "monetary" for entry in thermal)
 
 
+def test_m8_hot_water_discovery_payload_is_ha_energy_compatible(energy_db) -> None:
+    """Hot-water Meter discovery exposes the exact HA Energy Water metadata."""
+    from app.integrations.expose import build_catalog
+    from app.services.ha_discovery import build_discovery_payload
+
+    now = datetime.now(timezone.utc)
+    with Session(energy_db) as session:
+        _source, _channel, meter = _make_thermal_source_and_meter(session, "hot_water", now)
+        session.commit()
+        entries = {item.entity.key: item.entity for item in build_catalog(session)}
+
+    for suffix in ("total", "today"):
+        entity = entries[f"meter.{meter.uuid}.{suffix}"]
+        topic, payload = build_discovery_payload(entity, "homeassistant")
+        assert payload["device_class"] == "water"
+        assert payload["unit_of_measurement"] == "m³"
+        assert payload["state_class"] == "total_increasing"
+        assert payload["unique_id"] == f"{meter.uuid}_meter_{meter.uuid}_{suffix}"
+        assert payload["device"]["identifiers"] == [f"home-automation:meter:{meter.uuid}"]
+        assert topic == (
+            f"homeassistant/sensor/{meter.uuid.replace('-', '_')}/"
+            f"meter_{meter.uuid.replace('-', '_')}_{suffix}/config"
+        )
+
+
 def test_m8_meter_getter_hides_stale_or_offline_source(energy_db) -> None:
     from app.integrations.expose import build_catalog