earth_waterClean water is essen­tial to food pro­duc­tion. From irri­ga­tion through pro­cess­ing and prepa­ra­tion, the water used must be free from bio­log­i­cal, chem­i­cal and sed­i­men­ta­ry contaminants.

Vol­un­der has devel­oped a flex­i­ble design for mul­ti-stage water fil­tra­tion sys­tems. Our lat­est design includes a biosand fil­ter and an acti­vat­ed char­coal fil­ter. The biosand fil­ter is effec­tive at remov­ing bio­log­i­cal con­t­a­m­i­nants, such as pro­to­zoa, bac­te­ria (includ­ing E. coli), and some virus­es from the source water. The char­coal fil­ter is effec­tive at remov­ing chlo­rine, ben­zene, sol­vents and many pes­ti­cides and her­bi­cides. Both fil­ters remove sed­i­ment, reduce tur­bid­i­ty and improve odor and taste.

The fil­ter struc­tures are built from sched­ule 40 pvc. Each has a 4″ lay­er of coarse rock (~1″ diam.) at the bot­tom fol­l­lowed by a 4″ lay­er of grav­el (~1/4″). The final lay­er depends on the fil­ter type. In the biosand fil­ter there is a 12″ lay­er of sand while in the char­coal fil­ter there is a 12″ lay­er of acti­vat­ed char­coal, in our case made from coconut shell.

The fil­ters can be joined togeth­er to form a robust fil­tra­tion capa­bil­i­ty with a small foot­print and eco­nom­i­cal ener­gy usage. In this case, the biosand fil­ter must come before the char­coal fil­ter, as it is the slow­er of the two.


Plans are being devel­oped for an ultra­vi­o­let fil­ter stage, which would have an effect sim­i­lar to the biosand fil­ter but would have a greater through­put at the expense of greater ener­gy consumption.

The hapi plat­form is being extend­ed to pro­vide native sup­port for fil­ter man­age­ment, using lev­el switch­es and a small pump. This will be includ­ed in the v2.0 final release.

Here is the design for base mod­el filters:


The 3D mod­el file is avail­able upon request.

HAPI (Hydro­ponic Automa­tion Plat­form Ini­tia­tive) is an open-source project of Maya Cul­pa, LLC.

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