The frequency with which you need to refill water in a forklift battery depends on various factors, including the type of battery, the ambient temperature, usage intensity, and the charging method. Generally, you should regularly check the water level and refill if necessary. Here are some general guidelines:

1. Check the water level regularly: It is recommended to check the water level in the battery weekly. This can be done by removing the caps from the battery cells and visually checking if the electrolyte level is above the plates.

2. Refill water if necessary: If the water level in the battery cells falls below the recommended level, you should refill with water. Add only distilled water to avoid contaminants and minerals that could damage the battery.

3. Keep the water level within the correct range: Each battery has specific recommendations regarding the water level. Generally, the electrolyte level should be approximately 10-15 mm above the plates. Refer to the manual or the manufacturer's instructions for the correct water level requirements.

4. Be careful when refilling: When refilling water, you should be careful not to spill water on the battery or the electrical connections. Use a funnel or a special filling system to ensure controlled refilling.

Please note that the frequency of refilling may vary depending on the specific battery and the conditions under which the forklift is used. It is advisable to follow the instructions of the battery and forklift manufacturer regarding water refilling. They may have specific recommendations based on the battery type and other factors.