Is Drinking Rainwater Safe?

Recent evidence indicates that consuming rainwater may pose more risks than previously recognized. Many people assume that rainwater is similar to tap water, but it contains various microscopic impurities. These are filtered out before tap water enters homes.

Contaminants in Rainwater

Rainwater can harbor numerous contaminants. According to the Centers for Disease Control and Prevention (CDC), potential harmful substances include bacteria, viruses, parasites, dust, smoke particles, and various chemicals. Rainwater collected from rooftops may contain animal waste like bird droppings. Additionally, old roofs or drainpipes could leach materials such as asbestos, lead, and copper. Open containers can also gather insects and decaying organic matter, which increases health risks. Due to these concerns, the CDC advises against drinking collected rainwater, suggesting alternate uses like watering plants.

Variability of Contaminants

The levels of the contaminants in rainwater can differ significantly based on the region. Therefore, the risk of illness correlates with the amount of rainwater consumed. Proper handling of rainwater, including using a clean collection system and sterilizing the water through methods such as boiling or chemicals, may reduce harmful impurities. This has resulted in confusion regarding rainwater's safety for consumption.

New Risks: PFAS

More recently, scientists have identified a new risk factor associated with rainwater: toxic PFAS (per- and polyfluorinated alkyl substances). A study from August 2022 published in the journal Environmental Science & Technology found that rainwater globally holds concentrations of PFAS that surpass health guidelines. Thus, untreated rainwater likely is unsafe to consume.

PFAS encompasses over 1,400 man-made chemicals once commonly used in various products, such as textiles and firefighting foams. The current understanding of PFAS toxicity primarily comes from studies of four specific compounds known as PFAAs (perfluoroalkyl acids). These inclusively assess chemicals like PFOS (perfluorooctanesulfonic acid) and PFOA (perfluorooctanoic acid). Previous research demonstrated that these chemicals can cause various health issues, including cancer and complications during pregnancy. They may also harm the immune system and negatively affect vaccines in children.

Regulatory Responses to PFAS

Given the severe toxicity of PFAAs, many have been banned or restricted over the past three decades, except in specific regions like China. Regulatory guidelines have also been revised to account for the extreme dangers posed by these chemicals. For instance, the U.S. Environmental Protection Agency (EPA) significantly reduced the safe exposure level for PFOA.

PFAS have become known as "forever chemicals" because they do not easily decompose, lingering in the environment and maintaining their toxicity.

Rainwater Contamination Findings

In the study, researchers analyzed global rainwater samples and detected PFAS above safety limits established by regulatory agencies, including the EPA. Despite expectations that levels might decline, it appears the situation has worsened. The scientific community views PFAS concentrations as a new environmental boundary that we may have surpassed.

Notably, PFOA levels were at least ten times higher than the EPA's safety benchmark across all sampled locations, including remote areas like the Tibetan Plateau and Antarctica. The researchers are still exploring how PFAS travel to these distant regions, with theories suggesting ocean spray may play a role.

Potential Public Health Implications

The long-term public health consequences of PFAS-laden rainwater remain uncertain. However, exposure levels may have already been significant over the past 20 to 30 years. In developing countries where rainwater serves as the primary drinking source, the impacts are likely more substantial. Even certain developed areas still rely on rainwater for consumption.

Treatment Limitations

Even properly treated rainwater may not guarantee the removal of PFAS. These chemicals might also be present in tap or bottled water, but they generally exist at safer concentrations. However, While levels of PFAS will decline as they travel into the ocean, this natural process may take decades.

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