Name the number of sement d for solar water heaters 
CREATE TABLE table_15187735_18 (segment_d VARCHAR, segment_b VARCHAR)
SELECT COUNT(segment_d) FROM table_15187735_18 WHERE segment_b = "Solar Water Heaters"
<s>[INST] Write mssql query to answer the following question given the database schema. Schema: CREATE TABLE table_15187735_18 (segment_d VARCHAR, segment_b VARCHAR) Question: Name the number of sement d for solar water heaters  [/INST] SELECT COUNT(segment_d) FROM table_15187735_18 WHERE segment_b = "Solar Water Heaters" </s>