A DIY Water Filter

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pre-filter

pre-filter

For those of you unfamiliar with Baja fuel filters, they are multi-layer strainers, purchased or handmade, used to filter diesel fuel of dubious pedigree before loading. Water, whether from a dockside hose or rainwater, presents a similar challenge. Weve been exploring freshwater filtration possibilities for a series of articles to come, and while there are great pre-filtration products out there, none offer the versatility of our own home-grown solution, which we call the Baja water filter.

Cartridge filters are bulky, and while they are good for inline filtration at-the-dock systems, they also are susceptible to contamination since the greatest source of contamination is the junk growing in the hose itself. Hose-end filters are convenient, but the filtration is often coarse (10 to 40 microns), and they plug up easily, reducing flow to 2 to 3 gallons per minute after only a few fillups. With a few scraps of PVC pipe, simple tools, and common skills, a 4-inch by 14-inch, 1-micron bag filter becomes a multipurpose Baja filter serving all cruiser pre-filtration needs.

What Youll Need

The total cost for all parts is approximately $25. Heres what youll need:

1-micron polyester bag filter, seamless, trade size 4 (McMaster/Carr, 9316T211, specify 1-micron)
2 feet of 4-inch diameter PVC DWV pipe
2-inch by 3-inch reducer
2-inch by -inch NPT bushing
-inch by -inch NPT nylon barb fitting
Silicone caulk
PVC cement

No. 4 polyester felt filter bag

Construction

The 4-inch PVC pipe is small enough to support the top ring of the bag filter, yet large enough to give the bag an easy fit and good flow. To form an internal funnel and a bottom that can sit flat over a deck fill plate, slide the 2-by-3-inch concentric reducer about 5 inches inside the funnel (grind off small tabs that interfere). Seal the reducer in place with silicone caulk.

Next, glue a 2- by-3/4-inch NPT bushing into the reducer with PVC cement. The end of the bushing should be recessed about a half-inch from the end, so the funnel can sit on the deck plate without wobbling. Cut the 4-inch pipe long enough for the bag to hang free plus about 1-inch for stretch-about 15 inches inside the pipe. Insert a 3/4-inch PVC threaded nipple when used over the deck plate, or a 3/4-inch barb adapter for collecting rainwater. Smooth all edges, and add small holes near the mouth to hang from the gutter to collect rainwater.

In Use

Hose water: Drop it in the freshwater deck plate and watch the junk shed from the hose accumulate.

Rainwater: 1-micron filtration produces tank-quality water; rinse the salt and major bird bombs off your collector first.

Jerry cans: Upgrade water pulled from a grimy tap.

Clean: The bag can be laundered several times.

Sanitize: The bag can be dried and sanitized in the sun.

There are many bag filter materials and sizes available; weve tried them all and find polyester felt to offer the best economy and best removal efficiency of the particles of interest; it has something to do with surface charge and texture. While coarser bags promise more flow, the difference is small and the 1-micron filtration removes more silt and colloidal dust, ensuring a clean tank. There are also lighter versions using garden drain pipe instead of PVC for the main body; nipples and reducers can be adjusted for better flow rates or to tap into existing plumbing.

Darrell Nicholson, editor of Practical Sailor, grew up boating on Miami’s Biscayne Bay on everything from prams to Morgan ketches. Two years out of Emory University, after a brief stint as a sportswriter, he set out from Miami aboard a 60-year-old wooden William Atkin ketch named Tosca. For 10 years, he and writer-photographer Theresa Gibbons explored the Caribbean, crossed the Pacific, and cruised Southeast Asia aboard Tosca, working along the way as journalists and documenting their adventures for various travel and sailing publications, including Cruising World, Sail, Sailing, Cruising Helmsman, and Sailing World. Upon his return to land life, Darrell became the associate editor, then senior editor at Cruising World magazine, where he worked for five years. Before taking on the editor’s position at Practical Sailor, Darrell was the editor of Offshore magazine, a boating-lifestyle magazine serving the New England area. Darrell has won multiple awards from Boating Writer’s International, including the Monk Farnham award for editorial excellence. He holds a U.S. Coast Guard 100-ton Master license and has worked as a harbor pilot and skippered a variety of commercial charter boats.

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