Water filters for a house in Costa Rica

Most houses on this coast have a row of filter housings somewhere between the meter and the kitchen. They are easy to forget, because water keeps coming out of the tap whether they are working or not. Each one does a different job, and each has its own schedule.

Know where the water comes from

A house here is usually supplied by the national water institute, AyA, by a community water association known as an ASADA, or by its own well or spring. The first two are operators regulated under Costa Rica's drinking water quality rules, and it is reasonable to ask your ASADA for its latest test results. A private well or spring has no operator: the owner is the one responsible for testing it.

For private wells the United States Centers for Disease Control and Prevention advises testing at least once a year, for bacteria and nitrates among other things, and again after flooding. What a house needs in the way of filters depends on that answer, so the test comes before the equipment.

What each filter does

A sediment filter is a strainer. It catches sand, silt and rust, protects everything downstream, and does nothing about germs or chemicals. It tells you when it is full: the pressure in the house drops. In the rainy season, water from springs and surface sources often carries more sediment, so cartridges clog sooner than the calendar says.

An activated carbon filter improves taste and smell and removes chlorine. It is not a disinfectant. Carbon that has been left in place too long becomes a place for bacteria to grow, feeding on what the filter has collected, which is why it is changed on schedule even when the water still tastes fine.

An ultraviolet unit is the one that deals with germs. Water passes a lamp whose light inactivates bacteria, viruses and parasites. It removes nothing: no sediment, no chemicals, no taste. It also has three weaknesses. Cloudy water shields germs from the light, so a UV unit always sits after a sediment filter. The lamp weakens with use, and makers specify a new one every twelve months, or about 9,000 hours, even though the old one still glows. And it needs electricity: during a power cut, water passing through it is not being treated.

Reverse osmosis, usually a small unit under the kitchen sink, removes the widest range of contaminants and is the slowest and most demanding to maintain. For parasites such as Giardia and Cryptosporidium, the CDC's guidance is to look for reverse osmosis, a filter with an absolute pore size of one micron or smaller, or one certified for cyst reduction.

Reading the label

Filters are certified against standards written by NSF, and the number says what was tested. Standard 42 covers taste, smell and chlorine. Standard 53 covers contaminants that affect health. Standard 55 covers ultraviolet units, where Class A is built to disinfect and Class B is only for water that is already safe. Standard 58 covers reverse osmosis. A filter with no certification is a claim, not a test result.

Maintenance

The CDC puts it plainly: a filter has to be maintained to keep working and to prevent germs from growing in it, and that means changing cartridges as the manufacturer recommends. Filters collect what they remove, so whoever changes them should wear gloves and wash their hands afterwards.

In practice that means a date written on every housing, spare cartridges of the right size kept at the house, the sediment cartridge checked more often in the rains, and the UV lamp replaced yearly with its glass sleeve cleaned at the same visit. The new lamp is handled by its ends, never by the glass.

If the house has a storage tank

Not many houses here store water, but where there is a tank it needs cleaning, because stored water loses its chlorine and sediment settles in the bottom. The World Health Organization's technical note on the subject, which Costa Rica's Ministry of Health publishes in Spanish, gives the method. Drain the tank. Scrub the inside with detergent and water and rinse until no detergent remains. Fill it with a chlorine solution and let it stand for 24 hours. Drain it, refill with clean water and check with a test kit that the chlorine has fallen to 0.5 milligrams per litre or less before the water is used.

The note does not say how often. We found no official interval for household tanks in Costa Rica. Local service companies commonly recommend every six months, which is a sensible routine in this climate, and sooner if the water looks or smells different. Nobody should climb inside a tank alone.

This article explains what the equipment does. What your house needs depends on a test of its own water, and the dosing and installation are work for a qualified technician.