Vaginas also excrete discharge though, not just sweat.
Why do people always say this? EVERY HEALTHY vagina has a balance of bacteria in it. The way this bacteria reacts with hormones and oxygen produces a smell and an acidic environment. Vaginas are acidic, much more so than water which is mostly neutral but can teeter on either side slightly. Basic science would tell you there’s no way p*ssy tastes like water. Bacteria also has a smell, and it doesn’t smell like water. Acids are characteristically sour, obviously the extent of this sour taste is dependent on the woman, but if her vagina is healthy it’s acidic.
The only way a vagina has no scent or taste is through douching. Cervical mucous (the wetness) may have no taste/smell, but vaginal discharge, which every woman has, is filled with bacteria and skin cells.
Using douches and sprays throws off the ph which leads to an imbalance in normal flora leading to putrid smells. There are douches that aim to restore normal ph levels, but using things like peroxide (whose chemical composition is the same byproduct of some lactobacillus species in the vagina) or plain yogurt which contains lacto are things that can remedy that.
The only way p*ssy is sweet like someone said upthread, is because the woman most likely has diabetes. This will also lead to high incidence of yeast infections and bacterial vaginosis because of all the sugar present feeding bacteria.