Having two sinks in a master bathroom is either a nice little luxury, or a total relationship-saver, depending on how much your schedules overlap, how well you share space when they do, and just how messy you both are. Would anyone turn an extra one down? Turns out this set up does have a couple of drawbacks however, which might give you pause.
First, the Pros
There's lots to love about having his/his, his/hers, or hers/hers sinks. Above (and lead image), Emily Henderson used a pre-fabricated vanity from Wayfair with two sinks in her master bathroom renovation. She and her husband don't have to stare at each other's dried toothpaste, or argue about leaving hair in the bowl. This one's also got plenty of storage down below, and there's just enough space for a tray for products and accessories up top. Which means these two are pretty much winning at life right now.
Con #1: Two Sinks Vs. One Sink Cost
The first, most obvious one, is the added cost of installing two sinks versus one. It stands to reason that your renovation budget would increase — larger vanity, more fixtures to buy, and more areas to plumb.
This basic single vanity from Home Depot, with integrated counter and sink retails for $179. Add in a pretty basic faucet for $44 and you're looking at $223, before the cost of labor. (I estimate it would be about $150 to plumb a sink and faucet, depending on where you live and the full scope of the job of course).
The same model, in a larger two sink size, is $649. Combine two of the same faucets, for $88, and it jumps to $737, just for supplies. Add in the cost of plumbing labor for the extra faucet and sink, and that's probably another $300-500. During a recent renovation, Cassity of Remodelaholic switched hers over and actually opened up the wall to change out the plumbing (which isn't technically necessary, but looks a lot better underneath the vanity). She documents the whole affair if you want to see her process. Obviously, these costs can vary greatly, depending on how high-end or custom you go.
Con #2: Opportunity Cost
Unless you have an endless amount of space, you are giving up something else in order to get a second sink. Before you pull the trigger, ask yourself if you'd rather have a shower stall instead, or some other feature, like laundry. The Massachusetts home above, designed by Hamilton Design Associates, opted for a single sink, although (without seeing the room measurements), there's arguably space enough for two. You can see they chose to have a washer/dryer on the other side of the room here, which a huge boon in a small space.
And speaking of size, make sure you actually have the room to begin with. Buying a pre-fabricated vanity is a good way to ensure you've got the needed space between two sinks, without knocking elbows with your bathroom mate. You don't want two of you wedged in some tiny alcove. If you are creating your own double vanity situation, this means knowing the building code. (I believe the necessary distance between the centerlines of two side-by-side sinks is at least 30 inches. The minimum distance between the edges of two freestanding or wall-hung sinks is 4 inches.)
Reduced Counter Space & Storage
Again, this might not be a factor if you have other storage options in the bathroom. But know that a second sink definitely takes a bite out of your counter space, especially if you are the type of person who likes having a bunch of products easily in reach. The added plumbing down below also takes away from storage underneath a vanity. If space is already tight, factor this into your decision making process.
On the other hand, the sink in this bathroom from Arent & Pyke has empty countertops for days. In fact, the offset mirror almost creates a vanity table. All this means there's nothing getting in the between you and your hairdryer and lotions.