The most accurate method for determining the water content of soil is the oven drying method.

Here's a detailed explanation of this method and its advantages over other methods:
Oven Drying Method:

The oven drying method is a standard laboratory procedure used for determining the water content of a soil sample. This method involves drying a soil sample in an oven at a constant temperature (usually 105°C to 110°C) for a specified period (usually 24 hours) and comparing the mass of the soil before and after drying. The water content is then calculated as the ratio of the mass of water lost to the mass of the dry soil.

Procedure:
1. Weigh a clean, dry, and empty container.
2. Place a representative soil sample in the container and weigh the container with the sample.
3. Place the container with the sample in the oven and heat it at a constant temperature (105°C to 110°C) for 24 hours.
4. After 24 hours, remove the container from the oven and allow it to cool in a desiccator to avoid absorption of moisture from the air.
5. Weigh the container with the dried soil sample.
6. Calculate the water content using the formula:

Water content (%) = [(Wet mass - Dry mass) / Dry mass] x 100

Advantages of the Oven Drying Method:
- It provides highly accurate and consistent results.
- It is a widely accepted and standardized method, which allows for easy comparison of results across different labs and studies.
- The method is applicable to a wide range of soil types and conditions.

Comparison with Other Methods:
- Sand Bath Method: This method involves heating a soil sample in a container surrounded by sand. Although it is a relatively simple method, it may not provide accurate results due to uneven heating and the potential for contamination from sand particles.
- Alcohol Method: This method uses alcohol to replace the water in a soil sample, and the water content is determined by the difference in mass before and after alcohol evaporation. However, this method can be less accurate than the oven drying method because alcohol may not completely replace all the water in the sample.
- Calcium Carbide Method: This method involves the reaction between calcium carbide and water in a sealed container to produce acetylene gas. The pressure of the gas is proportional to the water content of the sample. Although this method is quick and can be used in the field, it can be less accurate than the oven drying method due to potential errors in gas pressure measurements and the sensitivity of the reaction to sample preparation and handling.

In conclusion, the oven drying method is the most accurate method for determining the water content of soil due to its high precision, consistency, and applicability to various soil types.