diff --git a/domain/sap10_calculator/rdsap/cert_to_inputs.py b/domain/sap10_calculator/rdsap/cert_to_inputs.py
index cd68d5099..ecb72917c 100644
--- a/domain/sap10_calculator/rdsap/cert_to_inputs.py
+++ b/domain/sap10_calculator/rdsap/cert_to_inputs.py
@@ -7698,9 +7698,16 @@ def _fuel_cost(
         if main_2_fuel_code is not None
         else main_1_high_rate_gbp_per_kwh
     )
+    # When DHW is supplied by a community heat network (WHC 901/902/914 on a
+    # heat-network main), the network heat — space AND water — bills at the
+    # main's Table-12 heat-network rate, NOT the cert-lodged HW fuel (which
+    # Elmhurst defaults to "Mains gas"). Mirror the .173 inherit already applied
+    # on the legacy/off-peak HW-rate paths (`_hot_water_fuel_cost_gbp_per_kwh`)
+    # into this §10a STANDARD-tariff path, which is the one that drives (255)/SAP.
     water_high_rate_gbp_per_kwh = (
-        table_32_unit_price_p_per_kwh(water_heating_fuel_code)
-        * _PENCE_TO_GBP
+        _fuel_cost_gbp_per_kwh(main, prices)
+        if _is_community_heating_hw_from_main(epc)
+        else table_32_unit_price_p_per_kwh(water_heating_fuel_code) * _PENCE_TO_GBP
     )
     # Secondary fuel cost: route through the cert's `secondary_fuel_type`
     # when lodged (e.g. mains-gas fire SAP code 605 → fuel 26 → Table 32