Madonna has been quietly renting a secluded, $6 million mansion in Water Mill since January, reports The Post’s Jennifer Gould Keil. The 8,500-square- foot, seven-bedroom home sits on three acres. Madge’s rental mansion on Blank Lane has two fireplaces, a great room, media room, dining room and chef’s kitchen, plus a tennis court and pool. She also has a $32 million Upper East Side mansion and the $5 million Bridgehampton horse farm she bought in 2009 from Kelly Klein.