A urine drug test is used to detect the presence of illegal and prescription drugs in urine. It’s also known as a urine drug screen.

In a urine drug test, a sample of urine is sent to a lab. A tester analyzes the urine for certain drugs or their metabolites. Metabolites are byproducts formed by the body after it processes a drug.

The urine shouldn’t contain too much or too little water. Otherwise, the results of the drug test might be inaccurate.

Diluted urine occurs when there’s too much water in the urine. It means the urine’s concentration is weak. As a result, the tester will be unable to properly detect the presence of drugs in the urine.

If you’re an employer who requires drug tests, you might wonder what causes diluted urine. This article explains the potential reasons of urine dilution and how to get accurate results.

Urine can become diluted due to many reasons. It’s not always because someone is trying to “cheat” the test by drinking lots of water. It can happen accidentally.

Possible causes of diluted urine include the following.

Drinking fluids for health reasons

Many people recognize the importance of staying hydrated. So, it’s common for individuals to frequently drink a lot of water.

If they regularly consume large amounts of fluid, their urine might be diluted.

Preparing to give a urine sample

If a person is unable to provide enough urine, they might have to return or repeat the test. Some people might drink lots of fluid beforehand to ensure that they can give a urine sample.

Taking diuretics

Some prescription medications have a diuretic effect. They increase urine production, resulting in diluted urine.

Drinks like coffee and tea are also diuretics.

Kidney problems

The kidneys remove waste from the body by making urine. If the kidneys aren’t working properly, they might release too much water in the urine.

Diluted urine usually has a lighter color than normal urine.

Additionally, testers can determine if the urine is diluted by referring to measurements called validity checks. These checks include urine creatinine and specific gravity.

Urine creatinine

Creatinine is a waste product that’s produced by your muscles. It’s made during the breakdown of creatine, an amino acid.

Your kidneys remove creatinine through the urine. The amount of creatinine in your urine indicates its concentration.

The normal range is between 20 and 400 milligrams per deciliter (mg/dL). In diluted urine, the urine creatinine level is between 2 and 20 mg/dL.

Specific gravity

Urine specific gravity indicates the concentration of urine. It compares the water content to the amount of substances in the urine.

Normal urine has a specific gravity of between 1.002 and 1.030. If the urine is diluted, the specific gravity is between 1.001 and 1.003.

To prevent diluted urine, you can set guidelines for urine drug tests:

  • Ask the people being tested to limit their fluid intake before the test.
  • Ask them to avoid diuretics, like coffee and tea, before giving a sample.
  • Collect the urine early in the morning.
  • If their job requires frequent hydration, collect the urine sample before work.
  • Schedule urine drug testing randomly.

There are two kinds of urine drug tests.


An immunoassay (IA) is a drug test that uses antibodies to detect the presence of certain drugs. Antibodies are proteins that bind with antigens, or foreign substances. In this case, the antigen is the drug.

In an IA, the tester adds the drug and drug-specific antibodies to the urine. If the drug is already in the urine, it will compete with the added drug to bind with the antibodies. This reaction means the sample is positive.

If the urine has no trace of the drug, the reaction won’t be significant. The sample will be considered negative.

An IA is inexpensive and quick. It’s usually used for initial testing. However, it’s unable to detect certain drugs. This means it can yield false positive or false negative results.

Gas chromatography-mass spectrometry

Gas chromatography-mass spectrometry (GC-MS) is used to confirm IA results. It’s more specific than IA, so it’s less likely to provide false results.

In GC-MS, a gas is added to the urine sample. The gas interacts with the substances in the urine, causing them to separate. The tester uses a machine called a mass spectrometer to detect the separate compounds.

GC-MS is the standard test used for follow-ups. Other types of chromatography may use liquid to separate the compounds.

Diluted urine can make it difficult to get accurate results from a urine drug test.

However, it doesn’t necessarily mean that someone is trying to “cheat” the test. Some people might drink lots of water to stay healthy or ensure they can give enough urine.

Certain medications and kidney problems can also cause urine dilution.

To prevent urine dilution, limit water and diuretic intake before administering the test. You can also collect urine in the early morning or before work.