The NLRP3 inflammasome is an essential component of the innate immune system, but excessive activation can lead to inflammatory diseases. Ion fluxes across the plasma membrane or from intracellular stores are known to regulate NLRP3 inflammasome activation. Deep-sea water (DSW) contains high concentrations of many mineral ions, which could potentially influence NLRP3 inflammasome activation. However, the impact of DSW on NLRP3 inflammasome activation has not been investigated. Here, we demonstrated that DSW with water hardness levels up to 500 mg/L did not affect cell viability or the expression of NLRP3 inflammasome components in macrophages derived from THP-1 cells. However, the DSW significantly inhibited IL-1β secretion and caspase-1 activation in response to NLRP3 activators such as nigericin, ATP, or monosodium urate (MSU) crystals. Mechanically, it was discovered that the presence of 5 mM magnesium ions (Mg2+), equivalent to the Mg2+ concentration found in the DSW with a water hardness of 500 mg/L, inhibits NLRP3 inflammasome activation. This indicates that Mg2+ contributes to the mechanism by which DSW mitigates NLRP3 inflammasome activation. Moreover, DSW administration effectively lessens MSU-triggered peritonitis in mice, a commonly used model for examining the impacts of NLRP3 inflammasome activation. These results show that DSW enriched with Mg2+ could potentially be beneficial in modulating NLRP3 inflammasome-associated diseases.