You can drink water before taking blood for kidney function test, but it should be in moderation, and generally it will not affect the test result. Kidney function test is mainly used for the diagnosis and screening of kidney related diseases, kidney function test includes blood creatinine, blood urea nitrogen, uric acid and so on. Drinking moderate amount of water will not affect the result of kidney function test, but you should have a light diet one day before the test, don’t drink alcohol, overeat or overwork, and fast for more than 8 hours before the test. Kidney function test not only reflects the excretory function of kidney, but also guides clinical medication and treatment. Patients should actively cooperate with the physician to make good preparation before the test so as to avoid wrong results. If there is any abnormality in renal function test, it is recommended to go to regular hospitals in time to avoid aggravating or delaying the condition.