What is the quickest way to treat a urinary tract infection?

Antibiotics. In the bad old days, common bladder infections were one of the common causes of death, especially in young women. Today's antibiotics changed this, and drinking plenty of water and taking cranberry juice or capsules may help. Especially, find out whether you have a predisposing factor -- stone, diverticulum, malformation -- and see if this can be addressed.
UTI treatment. Go to a physician, have a urine sample sent of for a culture and sensitivity and get started on antibiotics. That is the quickest way to treat a uti.