Sodium tungstate (Na2WO4) is soluble in water. Normally, sodium tungstate does not form a precipitate in water. It dissociates into tungstate ions (WO4^2-) and sodium ions (Na+) to form a uniform solution.

However, if the conditions in the solution change, such as a drastic change in pH (such as acidification) or the addition of certain specific metal ions, the tungstate ions may react with other substances to form an insoluble precipitate. For example:
1. Under acidic conditions, tungstate ions will combine with hydrogen ions (H+) to form tungstic acid (H2WO4), which has a low solubility in water and is easy to form a precipitate.
2. Certain metal ions such as calcium ions (Ca^2+) or barium ions (Ba^2+) may combine with tungstate ions to form an insoluble tungstate precipitate.
Therefore, under neutral or weakly alkaline conditions, sodium tungstate is soluble in water and will not form precipitate.