One thing to remember is that pets will spill some water, so I would have some margin of error there.

As for 4L/day, that's not a lot. Sure, if you are sitting in an airconditioned office and pounding a keyboard every day, you'll sweat out less than that, but if the stuff hits the fan, you'll probably have to do "some" manual labor. For Singapore, typhoons, maybe some seismic risks? All of those will require a lot of grunt work, and I know from previous experince that even if you "acclimate" to it, you can burn through three quarts per day no problem. And that's just to drink. Add in cooking water, toothbrush water, a reserve for first aid needs, and you've got the four liters and maybe a bit more.

Also, keep in mind that a lot of shelf stable food uses salt as a preservative- it is going to increase your water intake.