are sure 100% its urine or they doing a mouth swab cause then ur in more trouble. problem with drinking alot of water is u will have a lack of vitamins and can they can tell easy uve been tring to flush. problem with most pills or detoxic cleans is that you will have a high nitrate level and again can be spotted easy. there is also the difference in a handheld ua and one sent to a lab. the hand held is going to be more sesitive and easier to fail, but wont show the nitrate and lack of vitamins. if its sent to a lab they are more leinant cause they can tell the actual level and wont fail u below a certain level but will show the nitrate and no vitamins. also to end this long blab make sure to only give them a sample from mid stream cause it is the least toxic of the stream.
