The 21-year-olds have both tasted first-team football at the Emirates Stadium in the past, and have played important roles in the reserves so far this season.
Former England Under-19 striker Watt has scored four goals in four games for the Gunners' second string this campaign, and has enjoyed several similar loan deals in the past, spending time at Leeds, Sheffield Wednesday, Crawley and Southend over the last two seasons.
Midfielder Eastmond played 14 games for Wycombe Wanderers last season, and has represented Arsene Wenger's first team on 10 occasions, including a Champions League fixture away to Shakhtar Donetsk.
|STRONG START FOR JOE DUNNE|
|6/5||Colchester are 6/5 with Paddy Power to beat Hartlepool on Saturday|
The pair are new Colchester boss Joe Dunne's second and third loan signings since taking over from John Ward on Thursday, with MK Dons striker Jabo Ibehre also bolstering the ranks for the struggling League One side.