Ceragrav model LP5

I am a missionary in Angola, Africa with a family of four. We host visitors frequently. I am interested in purchasing a Ceragrav model LP5. I understand that it can hold up to 5 candles. How many would be best for our family?

The LP5 comes with 2 elements which can produce 20 gallons, if needed, of fine filtered water in a 24hr period. Thats almost a gallon per hour.
Each additional element is an extra ten gallons per day.
Each Imperial Supersterasyl  element is good for 750 gallons. For a family of four depending
on how much water you use, two elements can last you 1 year before you need to replace them.