Primary irrigation methods vary across Southeast Asian countries due to differences in geography, climate, and agricultural practices. The following are common irrigation methods in some Southeast Asian countries:

1. Aqueduct irrigation: Many Southeast Asian countries use aqueduct systems to bring water from rivers, lakes, or reservoirs to farmland. This approach often requires complex water management and distribution systems to ensure an equitable water supply.

2. Pump irrigation: Pump irrigation is a common irrigation method, especially in low-lying areas or where a raised water source is required. Farmers use pumps to pump water into fields to ensure crops get enough water.

3. Drip Irrigation: Drip irrigation is a water-saving irrigation method that is often used in areas with limited water resources. It drips water directly to the roots of plants through pipes and drip irrigation heads, reducing water waste.

4. Sprinkler irrigation: Sprinkler irrigation systems use nozzles to atomize water into fields and cover large areas of land. This method distributes water efficiently, but some water may be wasted.

5. Rainwater Harvesting: In some Southeast Asian countries, rainwater harvesting systems are used to capture and store rainwater for irrigating farmland. This method is especially suitable for arid regions.

6. Groundwater irrigation: In some regions, farmers rely on groundwater sources for irrigation. They use wells or pumps to bring groundwater to the surface for irrigation purposes.

7. Tidal irrigation: In coastal areas, some farmland uses tidal irrigation. This approach uses the periodic rise and fall of the tides to bring seawater into the fields through a drainage system to remove salt and supply water.

The choice of these irrigation methods depends on land characteristics, water availability, climatic conditions and agricultural practices. Southeast Asian countries often use a variety of different irrigation methods to suit a variety of situations. In addition, with the development of science and technology, some countries are also experimenting with new irrigation techniques to improve the efficiency and sustainability of agricultural production.