A glass is filled with 6 x 4/5 = 24/5 ounces of water.
So, 10 6-ounces of glasses contains a total of 24/5 x 10 = <<24/5*10=48>>48 ounces of water.
To fill the 10 glasses to the brim, 10 x 6 = <<10*6=60>>60 ounces of water are needed.
Hence, 60 - 48 = <<60-48=12>>12 ounces of water are still needed.
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