Given solar showers use solar energy there is no definitive time it will take to heat up the water. There are serval factors that will contribute to this, including:

  1. Sunlight intensity: The stronger the sunlight, the faster the solar shower will heat up. On a sunny day with high solar intensity, it might take around 1 to 2 hours for the water in the solar shower to reach a comfortable temperature.
  2. Water Capacity: The volume of water in the solar shower will affect how quickly it heats up. Larger volumes of water will generally take longer to heat compared to smaller volumes.
  3. Initial Water Temperature: If the water you put into the solar shower is already relatively warm, it will take less time to reach a comfortable showering temperature compared to starting with cold water.
  4. Weather Conditions: Cloudy or overcast conditions will significantly slow down the heating process. On cloudy days, it might take several hours to or even most of the day for the water to heat up, and it might not reach as high a temperature as on a clear, sunny day.

A general estimate, under good sunny conditions, a solar shower might take around 1 to 4 hours to heat up, but this can vary widely based on the factors mentioned above. It’s always a good idea to set up your solar shower in a sunny and open area to maximise exposure to sunlight and to plan if you want to use it at a specific time.