Is waster a word in the Scrabble Dictionary

Yes, waster is playable

...and is worth 9 points.

Found in the following dictionaries

Enable (Words with friends)
SOWPODS (Collins Scrabble Words)
OTCWL2014 (NASPA Word List 2014)
TWL06 (NASPA List 2006)

"Waster" Definition

noun

One that lays waste; a destroyer: a waster of enemy cities.
One that wastes: a waster of time; a waster of money.
One that spends or consumes extravagantly and without thought for the future.
A dissolute person.
One that uses or causes or permits .