Zak Waters (born January 22) is an American musician, singer-songwriter and record producer. Born in Los Angeles, California, he is also prominently known by the stage name Pretty Sister. Waters began his music career forming the band Blueskyreality. After the group disbanded, Waters started his solo music career, releasing his debut extended play (EP), New Normal (2011).

He featured on Madeon's 2012 multi-platinum single "The City", to positive acclaim, charting at number 20 on the US Hot Dance Club Songs chart and number 16 on the UK Dance Chart. He released his debut studio album, Lip Service, on September 9, 2013. The following year, he released his second EP, Now // Later on Rostrum Records. He collaborated on Adventure Club's single "Fade", which became certified gold by the RIAA. He also collaborated on other popular singles including Adventure Club and David Solano's "Unleash (Life In Color 2014)" and Alex Gaudino and Manufactured Superstars's 2015 single "Lights Go Out". He appeared on the American songwriting competition series Songland in 2020.

As Pretty Sister, he has released one studio album, Catalina (2021), and three extended plays, Z Funk Era, Vol. 1 (2018), Poolside Vibe (2019), and 20 (2020). He has featured on other artists' singles including Nause's platinum-selling 2015 single "Dynamite" and Keljet's "Love At First Site" and LDN Noise's "Tears", which was released in August 2016. He has collaborated and produced for numerous other music artists such as Betty Who, Breathe Carolina, Nathan Sykes, Superfruit and JoJo, among others.