Hello, Welcome to Just Answer and thanks for your question. The etg will be below detectable levels in 5 days even if you had been drinking heavily prior to that. While water will increase the dilution, you have to be careful not to drink too much water. They will check specific gravity and creatinine and a too dilute sample is not a good thing either. They will assume you have been drinking and trying to beat the test.
If you have been drinking heavily, it probably will show up in 80 hours. You need the full 5 days for a negative result.
It would only show up after 5 days if someone had been soaked in alcohol beyond belief and had a metabolic disorder that slowed alcohol metabolism, or had been using other things that contain alcohol since stopping drinking (alcohol hand sanitizers, mouthwash, spray products). The amount of alcohol ingested is related to the amount of etg detected. Only if metabolic pathways are blocked would you see detectable quantities over 5 days though.
It doesn't technically "accumulate." However, each day's alcohol will still be detectable and adds to the body's burden of etg. Etg should be gone in 5 days after the last drink though unless someone has a metabolic problem or has been using non-drinking alcohol.