Water treatment sludge (WTS) is a problematic waste produced from water treatment processes. WTS contains high in organic (e.g. nutrients) and inorganic (e.g. heavy metals) pollutants. There are many treatments of sludge. Current treatments of sludge are either by chemical, physical or biological treatments. However, the treatments require high energy level and expensive. Therefore, solidification method is introduced since the production of WTS is increasing. Solidification able to transform the physical forms of the sludge and depends on the type of binder used. In this study, calcium carbonate powder (CCP) was introduced as a binder to solidify WTS. The objectives of this study are to investigate the potential of CCP as binder in solidifying WTS and to obtain the optimum percentage of CCP as cement replacement material to solidify WTS. CCP was used to replace Ordinary Portland Cement (OPC) at 10%, 20%, 30% and 40%. The solidified WTS was cured under water curing for 1, 3, 7 and 28 days. The effectiveness of using CCP as binder to solidify WTS was evaluated based on the compressive strength values. Results showed that the compressive strength of solidified WTS increased with increasing curing days. However, the compressive strength of solidified WTS was reduced proportionally with the increasing percentage replacement of OPC with CCP. In conclusion, 40% CCP contains in C5 was the optimum CCP replacement percentage. The 28-day compressive strength value of C5 was 0.62 N/mm2 and the value was exceeded the minimum allowable landfill disposal limit which is 0.34 N/mm2.