How to make a homemade water filter from two buckets

When the tap stops or a boil-water notice runs for weeks, a pitcher filter on the kitchen counter is the wrong tool. Those cartridges improve the taste of water that is already treated. They are not made to take pond water and make it drinkable. A gravity filter with a ceramic or carbon-block element is, and the boxed stainless versions cost several hundred dollars. The same design can be put together from two plastic buckets for well under a hundred.

What you will need

• Two 5-gallon food-grade buckets with lids. Bakeries, supermarket bakery counters and restaurants often give these away. Never use a bucket that has held paint, solvent or cleaning products.
• One or more gravity filter elements. These are the candle-shaped ceramic or ceramic-and-carbon cartridges with a threaded stem and a wing nut, the style popularized by the Berkey and British Berkefeld systems. Look for an absolute pore size of 0.2 micron or smaller and certification to NSF/ANSI Standard 53 for cyst reduction. NSF is NSF International, the standards body, whatever some sellers call it.
• A plastic spigot with a gasket and nut.
• A drill with a 1/2-inch bit and a 3/4-inch bit, or whatever sizes match the element stem and the spigot.
• A marker.

Element-and-spigot kits sold for bucket builds were around $30 in 2012, and branded elements alone still cost far less than a complete system.

How to put it together

1. Drill a 1/2-inch hole in the center of the bottom of the first bucket, which becomes the top, raw-water bucket. Drill one hole per element if you are fitting two or more, spaced so they do not touch.
2. Stand the top bucket on the lid of the second bucket and trace around each hole with the marker.
3. Drill a 1/2-inch hole through the lid at each mark, so the element stems will pass straight down into the lower bucket.
4. Fit the elements in the top bucket, stem down through the hole, with the rubber washer inside and the wing nut snug underneath. If the element came with a pre-filter sleeve, pull it on first.
5. Drill a 3/4-inch hole in the side of the lower bucket, an inch or two above the bottom.
6. Fit the spigot through that hole and tighten its nut against the gasket.
7. Snap the lid onto the lower bucket and seat the top bucket on it, lining the element stems up with the holes in the lid.
8. Pour water into the top bucket. Gravity pushes it through the ceramic, and a gallon or so collects below in about an hour, depending on the element and how dirty the water is.

Before the first use, flush a few gallons of tap water through new elements as the maker directs, and throw that water away. Label the top bucket “raw” and never let raw water touch the spigot or the inside of the lower bucket.

What a filter like this does and does not remove

A clean ceramic element makes cloudy water visibly clear. That shows it is catching sediment. It says nothing about germs, and clear water can still make people sick.

Filters with a pore size of 1 micron or smaller trap protozoa such as Giardia and Cryptosporidium. Elements rated around 0.2 micron also remove most bacteria. Viruses such as norovirus and hepatitis A are far smaller and pass through microfilters. Public-health guidance is therefore to filter first and then disinfect. Boil the filtered water for one minute, or add unscented household bleach at the doses in the EPA’s emergency disinfection guidance and wait 30 minutes.

Neither step removes fuel, pesticides, heavy metals or industrial chemicals. Floodwater and runoff from roads or farms should not be treated as a drinking source with this kit, whatever element is fitted.

Testing is not proof

Some reviews of these filters describe drinking stagnant swamp water through a budget element and feeling fine a week later. That tells you nothing reliable. Illness from waterborne parasites can take one to two weeks to appear, many infections cause no symptoms at all, and one person getting lucky proves nothing about the next glass. Do not test a filter by drinking from a source you believe is contaminated. Buy certified elements and add disinfection.

Taste and upkeep

Water from a still pond or from boiling tastes flat because it has lost dissolved air. Pour it back and forth between two clean containers a few times and the taste improves.

When the flow slows, lift the elements out and scrub the ceramic surface with a clean pad under treated water, following the maker’s instructions. Do not let a wet element freeze, and throw away any element that is cracked or chipped, because a hairline crack lets untreated water straight through.