The insulation in my roof is made from plastic bottles with an R value of 5.  Leaving aside the inconvenience, what depth of (empty) plastic bottles would I need to produce the same level of insulation?  Would the bottles need to be the same size and arranged, or could they just be thrown in randomly?

My local authority parks department proudly boasts that it uses recycled water, but isn't all water recycled?  Isn't there a finite amount of water on Earth and, if so, how often is each "piece" reused in human activity such as drinking, cooking, washing, agriculture and industry?