Home / Blog / Environment

Does rain clear the haze? What rain, rainwater and flash floods mean for you in Singapore

Hazy days and thundery showers are overlapping in Singapore right now. At 2pm on 16 October, the 24 hour PSI in the Central region was 228, in the very unhealthy band. Many people are asking the same two questions: will the rain clear the haze, and is the rainwater itself polluted? Here is what we found, and what we could not find.

Does rain clear the haze?

Rain helps. Raindrops capture suspended particles as they fall, and heavier rain works better, according to a researcher at the National Institute of Education (NIE). On 21 September, after rain, NEA's 24 hour PSI fell from 68 to 86 in the morning to 65 to 80 by 9pm, and 1 hour PM2.5 fell after afternoon showers.

The relief is often short. While fires keep burning in Kalimantan and southern Sumatra and the wind carries smoke towards Singapore, the haze can return once the rain stops.

The catch: mist after the rain

NIE also points out that in warm, humid weather, rainwater can evaporate and its moisture can combine with leftover PM2.5. This forms tiny droplets that hang near the ground and look like mist. The droplets can be several times larger than PM2.5 but can still affect health: larger ones can irritate the upper airways and cause cold like symptoms, and smaller ones can reach the lungs. A damp, hazy evening is not automatically a clean one.

Does haze pollute the rainwater?

Rain carries particles down to the ground, which is how it clears the air. What we could not find is a Singapore figure for how much dirtier rainwater becomes during haze, or Singapore advice on drinking it. We looked for numbers and did not find any, so we are not going to guess one.

Here is what we did find. In this haze, fine particles are doing the work: in all five regions at 2pm, PM2.5 was the pollutant setting the PSI, while sulphur dioxide stayed very low. That tells us what is in the air. It does not tell us what is in the rainwater.

The closest guidance we found is Australian advice for rainwater tanks after bushfires. It covers ash and debris from fires, not haze, and it gives precautions rather than figures. Tasmania Health suggests checking roofs and gutters, diverting the first flush of rain, and not drinking water that looks, smells or tastes unusual. A Flinders University study spiked water in a lab with fire related substances, not real rain, and concluded that such water is likely fine for uses like irrigation but not for drinking.

Our reading is simple: until there is better evidence, treat rainwater collected during haze as non drinking water. This is our interpretation, not official advice.

Thunderstorm and flood season

Thundery showers are common in Singapore at this time of year, and a heavy downpour can cause flash floods. PUB's flood safety tips are worth remembering:

• Do not drive through water deeper than the kerb, or where you cannot see the road markings.
• If your car stalls in floodwater, do not restart it. Turn on your hazard lights and call for help.
• On foot, avoid wading through water deeper than your ankles, and probe ahead for open drains.

What to check in PantauSivik

You can check the air, the sky and the alerts in a few taps before you leave.

1. Open Weather to see PSI and PM2.5 for your region, and how far away the lightning is.
2. Open Public Alerts for heavy rain, lightning and flood alerts where data is published. After heavy rain, the Alerts card shows "Heavy rain has eased" for 30 minutes.
3. Open Settings and switch on the Environment alert, so you hear when air quality gets worse or improves.

Read more: How to read weather, PSI, UV and heat stress in Singapore, How to use Public Alerts for floods, train faults, road works and more and Haze in Singapore, 2026 compared with 2023.

Common questions

Does rain clear haze for good?

No. Rain can bring a temporary dip, but while the smoke source continues, haze can return. Keep checking the PSI and PM2.5 readings.

Is rainwater safe to drink during haze?

We found no Singapore guidance saying it is. Australian advice for fire affected tanks says not to drink water that looks, smells or tastes unusual. Treat rainwater collected during haze as non drinking water.

What should I check before going out in a storm?

Check the Weather page for lightning, Public Alerts for heavy rain and floods, and your route before you drive.

Sources: NIE, 21 September 2026; Tasmania Health; Flinders University; PUB flood safety tips; NEA readings in PantauSivik, 16 October 2026, 2pm.

See also: Rain in Singapore for visitors, Four stormy days of lightning, Haze, heat and UV: check before you go.