user: Question: Name the number of sement d for Solar Water Heaters 
Columns: ['Series Ep.', 'Episode', 'Segment A', 'Segment B', 'Segment C', 'Segment D']
Types: ['text', 'real', 'text', 'text', 'text', 'text']
Sample row: ['18-01', 222.0, 'ed Pattern Glass Panels', 's Road Case', 'Stop-Frame Animation (Part 1)', 'Stop-Frame Animation (Part 2)']
SQL:

assistant: SELECT COUNT("Segment D") FROM "Table" WHERE "Segment B" = 'Solar Water Heaters';