Can drinking a lot of water before urine test alter the results if you think you have protein in urine. will that make results negative when its actually positive?

Could: Urine protein is measured just as mg/dL would be affected by drinking more water and making urine dilute. As a counterbalance to that if protein is measured with reference to urine creatinine concentration that can provide a corrective factor for dilute urine. If your doctor is concerned , s/he may ask you to collect 24-hour urine. for info visit this: https://www.aafp.org/afp/2000/0915/p1333.html