TEMPO.CO, Jakarta - Several social media accounts have posted an advisory urging Indonesian residents not to collect rainwater resulting from weather modification operations. These posters were circulated by Account 1 [archived] and Account 2 on Facebook, as well as Account 3 and Account 4 on Instagram. The posters state that rainwater produced through weather modification is potentially contaminated with chemical agents. These chemicals are claimed to be hazardous to health if the water is used for cooking, bathing, or drinking.
The Indonesian government employs weather modification operations to extinguish forest and land fires and to mitigate the effects of prolonged drought. Is it true that rain resulting from weather modification poses a health risk?
Fact Check
Tempo verified the content by comparing it with information from credible sources. The findings indicate that there is currently no recent research comprehensively testing the safety of rainwater produced by weather modification operations. However, previous studies suggest that weather modification does not have a significant impact on health or the environment. Research into the effects of weather modification must continue.
What Is Weather Modification?
I Putu Santikayasa, Secretary of the Center for Climate Risk and Opportunity Management in Southeast Asia and the Pacific at IPB University, explains that weather modification is a technique used to alter weather conditions without permanently changing the climate. The effects of this technique are only temporary. "It is the weather that is modified, not the climate," said Putu, as cited on the IPB University website on April 11, 2025.
According to him, there are several common methods of weather modification. The most prevalent method is cloud seeding, which utilizes salt to accelerate condensation within clouds, thereby inducing rainfall sooner. Another method is "cloud breaking," which is used to inhibit condensation and reduce rainfall intensity.
Various other advanced methods are currently being researched. However, weather modification efforts must still take into account atmospheric stability and the status of water vapor in the atmosphere. Weather modification—or artificial rain—has been conducted in Indonesia since 1977, following the adoption of techniques from Thailand. At that time, the focus was on supporting agriculture by filling strategic reservoirs for hydroelectric power plants or irrigation needs.
Since 2011, weather modification has been employed for disaster mitigation in response to the increasing frequency of hydrometeorological disasters, such as forest and land fires, landslides, and floods.
Stages and Materials for Weather Modification
Prof. Mangapul Parlindungan Hasibuan, a professor in the Department of Geography at the Faculty of Mathematics and Natural Sciences (FMIPA), Universitas Indonesia, stated that weather modification begins with monitoring atmospheric conditions using weather radar, satellite imagery, and data on wind direction, humidity, and air temperature. Only clouds with specific characteristics meet the necessary criteria.
"So, not all clouds can be seeded for weather modification," Mangapul told Tempo via WhatsApp message on Tuesday, September 15, 2026.
Once target clouds are identified, seeding materials are dispersed using aircraft or ground-based seeding devices. Common materials include sodium chloride (NaCl) salt—in the form of a solution or hygroscopic powder—calcium chloride (CaCl), urea, and hygroscopic-based flares.
These particles act as condensation nuclei where water vapor condenses to form water droplets. When the water droplets or ice crystals become sufficiently heavy, gravity pulls them down as rain. Mangapul emphasized that weather modification does not create rain from clear skies. "This technology works by utilizing existing clouds and favorable atmospheric conditions," he said.
Health and Environmental Impacts of Weather Modification
Budi Harsoyo, Director of Weather Modification Operations at the Meteorology, Climatology, and Geophysics Agency (BMKG), explained that studies on weather modification operations to date indicate no significant impact on the environment or human health. Previously, the BMKG formed a team to test water samples from six different locations in the Lake Toba area. Testing was conducted prior to the operation, during the first and second phases, and after the weather modification activities were completed.
The parameters measured included acidity levels (pH), electrical conductivity, and the presence of chloride, nitrite, nitrate, potassium, sodium, and magnesium ions. All test results were then compared against water quality criteria established by Government Regulation Number 82 of 2001. This regulation categorizes water quality into four classes: Class I for drinking water; Class II for water-based recreation and fish farming; Class III with more lenient standards; and Class IV specifically for agricultural irrigation.
Laboratory test results showed that the pH level of rainwater at the sampling sites was above 7. "This means the water is neutral to alkaline, not acidic," Budi Harsoyo told Tempo via WhatsApp on Tuesday, September 15, 2026. These findings align with the composition of the seeding materials used—namely powdered salt (NaCl) and potassium chloride (KCl)-based flares—neither of which contains SO2 or NOx compounds.
The World Meteorological Organization (WMO) has stated that studies conducted prior to June 2024 showed no significant impact on human health or the environment resulting from the use of silver iodide (AgI) or other seeding agents. However, the WMO noted that the use of seeding materials in significantly larger quantities, or the introduction of new materials, must be accompanied by an evaluation of their potential environmental and health impacts.
Conclusion
The claim that rainwater resulting from cloud seeding or weather modification operations is hazardous is unsubstantiated (no proof or evidence yet).
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