This study focused on the relationship between peatland catchment areas and aluminium (Al). For some major development areas in Sarawak, the only available water sources are peat waters. Thus, the objectives of this study were to quantify the levels of Al and other trace metals in raw and treated water from peat and non-peat sources and also to quantify the levels of organic matter and nutrients in raw water from peat and non-peat sources. The study was conducted at four selected catchment areas in Mukah, Sarawak. In particular, this study shows that the treated and raw water sources from both peat and non-peat sources have high levels of Al, ranging from 0.089 – 3.458 mg/L for raw water and 0.235 – 4.574 mg/L for treated water. In addition, results show that treated water from two of the peat water sources were significantly higher in mean levels of Al as compared to before treatment in both sampling trips. Treated water from non-peat source also was significantly lower in mean levels of Al than the treated water from peat sources. Low pH, a typical peat swamp water characteristic was shown to have a big impact on the levels of Al in treated water, mainly due to the higher solubility of Al in acidic condition, with the use of Al-based coagulants in its water treatment processes. Thus, considerations have to be made on the use of Al-based coagulants.