Wahii WaterSlide 75 - World&#39;s Biggest Backyard Lawn Water Slide! Kids love it! See the Wahii video on YouTube! 75ft long x 12ft wide. Initial set-up takes approximately 15 minutes... the slide is huge! The Wahii is constructed of thick specially formulated, UV protected plastic. Surface is extremely smooth and rated to hold 256lbs per square foot! Perfect lawn water slide for birthday parties.