Our first two tanks were poured concrete. They still work, but we will not build another one.
When we started, concrete looked like the obvious choice. It is cheap, local builders know it, and a concrete tank does not blow away in a typhoon.
What went wrong
Concrete tanks crack. Ours did not leak much, but hairline cracks let in light, and light grows algae. Concrete also needs a skilled mason and four weeks of curing on site, and on the islands that means four weeks of boat trips.
The water in a new concrete tank is alkaline for the first months too. The children said it tasted like the cement bags, and they were right.
What we build now
Since 2022 every tank is food grade polyethylene, in 5,000 litre units, set on a reinforced concrete base and strapped down against the wind. Two or three units are joined at the bottom when a school needs more storage.
A 5,000 litre unit costs about ₱25,000 delivered, crosses on an ordinary outrigger boat and goes up in a day. If one is ever damaged, we replace that one unit and the school keeps the water in the others.
What happened to the old tanks
Pagsalo’s concrete tank is still in use, lined with a food grade membrane since 2023. Tambisan’s was replaced by two plastic units and now holds water for the school garden.
The trade-offs
Plastic is not perfect. Sunlight breaks it down over the years, so every tank sits in the shade of the roof or under a simple cover. Plastic tanks are also light when empty, which is why every one is strapped to its base with steel bands and bolted down before the first rain.
A concrete tank, done well, can outlast a plastic one. But done well means a skilled mason, cement of good quality and time to cure, and on a small island those are hard to find at once.
What we tell other groups
Other groups ask us which to build. Our answer: if your tank can be reached by truck, and you have a mason you trust, concrete can work. If it has to cross the sea on an outrigger, use plastic units, and buy them all from one supplier so the fittings match.
The numbers
Our two concrete tanks cost about ₱38,000 each in materials and labour, for 10,000 litres. Two plastic units holding the same cost about ₱50,000 delivered, but went up in a day instead of a month, and needed no boat trips for curing checks.
