One question runs through the minds of new parents every day: Is this safe for my baby? With all household items under new scrutiny, tap water is no exception.

Drinking water is generally safe, so tap water is usually safe for babies–whether you’re mixing infant formula or they’re drinking from a sippy-cup. When there are contaminants, however, even trace amounts pose a higher health risk to babies than adults as babies are more sensitive than adults.

Common contaminants differ a lot based on where you live. Nitrates, for example, are especially prevalent in rural drinking water wells because of their use in fertilizers. Testing water is the only way to know for sure what contaminants are in your water, especially if your water comes from a well, where you have the responsibility to test and treat the water.

Infant health is a major predictor of future outcomes of well being—from adult health to success in school and at work. When so much is at stake, health at birth and for the first year of a child’s life is extremely important.

What’s more, infants are especially sensitive to water quality. They drink more relative to their weight than adults, and so the concentration of chemicals in their body relative to their body weight is higher.

Babies under six months shouldn’t drink plain water at all. If they are drinking formula, however, you often have to mix it with tap water. If your tap water is not safe, your baby will be exposed to contaminants in their formula mix.

In early infancy, babies undergo rapid development, so the impact on their organs and brains are more severe than on adults. In this critical stage, exposure to chemicals can also affect cognitive and physical development.

Babies bodies’ do not have high tolerances to chemical exposures, and thus they are less effective at processing and expelling harmful substances than adults.

Some contaminants are more common than others and pose a more present threat to infant health. When you’re testing your water with a new baby in the house, you should take a screening approach to scan for a variety of contaminants. However, there are a few common contaminants of particular concern: coliform bacteria, nitrates, and lead.

All of these have different adverse health impacts and require different treatment. Bacteria can cause flu-like symptoms and may indicate the presence of other viruses or parasites.

Nitrates are of particular concern for pregnant women and babies, as they can cause methemoglobinemia, also known as blue-baby syndrome. Methemoglobinemia causes severe oxygen deficiency, which can lead to cyanosis (skin discoloration) and, in extreme cases, suffocation.

Lead is toxic to children — it gets stored in bones and slowly releases over time. Its toxic effects can harm many different systems in the body.