When we were constructing our home here on the east shore of Sarangani Bay in southern Mindanao, we knew that a water supply would be a problem. There is no usable ground water here, and no surface water. So that leaves the rain. It did not take me long to find out that no one had any data on rainfall. If I wanted it, I would have to gather it myself, day by day, record it, and wait for some kind of picture to emerge. I began gathering data in December 2006, so now I have 25 months of data.

We have for a long time intuitively knew that storing rain water would be the way to go. So all our buildings have gutters and storage for the rainwater. Over time, the system has grown quite elaborate. A system of conduits that connect the various storage tanks, and drainage for the inevitable overflow. If it rains 75 inches a year, you could never hope to store that much water.

I began by buying a rain gauge from Edmunds Scientific. It was one that did just about everything imaginable, of course. It lasted about 6 months, then feature after feature went by the wayside. I knew I had to do something. I have a digital scale in the kitchen that is accurate to one gram. 1 gram happens to be the weight of 1/1000 of a liter of water. So if I measure the weight of water collected in 24 hours by a container with a known cross-sectional area, I could easily convert that weight into a depth of water falling in one day.

In 2008, 92.3 inches (234.4 cm) of water fell on our roofs. We have 506 square meters of roof, so the rainfall totaled 313,321 gallons. I think we have added roof area during the year, so I need to check that figure. But it doesn't really matter since we can't possibly store that much water anyway.

The data is interesting, statistically. Surprisingly, rainfall is pretty well distributed over the year. The longest dry spell in 2008 was 7 consecutive days. We had 18 days of rain in a row in Nov-Dec. Two storm events occurred, one in April when it rained 6.8", and one in December when it rained 5.2" in 45 minutes. Both storms produced flooding with muddy water entering our house. We have undertaken significant civil works since then to manage that a little better from now on.

Our storage capacity is not large enough to carry us through the dry spells, so we haul spring water about 2 miles using our flatbed truck and 55 gallon drums. We have the manpower for this, so we have a constant supply of water for all our uses, including watering plants when they need it.

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