Research Articles published by Desalination and water treatmenttigated. Water hardness has a significant impact on groundwater, especially in arid and semi-arid regions, leading to wasted investments in borehole drilling and worsening accessibility to potable water. In many developing countries, groundwater is the main source of drinking water. In this study, low cost and readily available cashew nut shells activated carbons (CNSAC) were used to remove hardness from groundwater in a column setting. The recommended design parameters for the packed-bed column were as follows: area (A) of 265.0 cm2 and diameter (d) of 18.4 cm, at a flow rate (Q) of 75.0 cm3 min–1. For the field hard water at a flow rate of 2.0 mL min–1, the recommended empty bed contact time was 70.7 min whereas the breakthrough time was about 430.0 min. Also for field hard water, the results showed that competing ions in the groundwater lowered the materials adsorption capacity. Results from this study indicated that CNSAC may be used to adequately remove groundwater hardness. Using these results, a filter was designed. The designed water hardness filter, which will be scaled up for point-of-use applications, may provide the much-needed solution to many people in most developing countries where similar field conditions prevail.