This is an irregular verb. It follows the conjugation pattern of the verb parecer.
Present:
Abastecen a toda la región con agua potable.
(They supply the entire region with clean water.)
Preterite:
Los camiones abastecieron la ciudad durante la emergencia.
(The trucks supplied the city during the emergency.)
Present Subjunctive:
Es importante que abastezcan comida con regularidad.
(It's important that they supply food regularly.)