To make sure you preserve the life of your pump and keep your indoor water wall fountain running properly, you'll need to keep the water capacity at an optimal level. Water fountains act as natural humidifiers in any environment. They lose water and add moisture to the air. How much water you need to add will depend on the environment you live in. Indoor fountains tend to be in a climate-controlled area, so it will have less water evaporation than an outdoor fountain in a dry area, like Arizona. The best way to maintain the correct water capacity is by adding a small amount of water on a daily basis rather than a few gallons every few days. For a guideline on the exact amount of water level your indoor water wall fountain needs, check with the fountain's instruction manual.