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I'd like to add a laundry sink in, well, the laundry room. The way the room is set up, I can't branch the supply directly from the washer supply (the washer is placed in a corner on the right and the main waste stack is behind the dryer, to left of the corner-bound washer). There is, however, a shower on the back side of the wall from the desired sink location. Is there anything wrong with branching the supply from the shower (teeing it off and continuing a line down the wall)? I attempted to Google the answer, but didn't quite know how to phrase it, thus finding no answer about mandatory terminal locations of water supply lines (or if that was even a thing to begin with).

I can see a potential problem with dominance of hot water to two sources on the same line, but the hot water heater is just feet down the line. The shower is the first thing to get said hot water, so I don't imagine the few times the laundry sink and shower are in use at the same time being more of an issue then the kitchen sink and the shower who's-more-important problem which exists in every place I've ever lived.

I've got drainage sorted out - and really the supply as well - I just want to make sure that branching from what is currently terminal at the shower is a "thing".

  • Since the sink and shower will both be served by the same water line and if both are being used at the same time neither will get a full water supply. – d.george Nov 15 '17 at 11:55
  • In a laundry sink you want high flow out the faucet. Laundry faucets generally do not have flow restrictors like bathroom faucets and showers. (You don't want to wait forever to fill a bucket.) The water lines to the bathroom are generally smaller (no more than 1/2"). I teed off bathroom lavatory lines to supply a utility sink in the garage and this has worked OK, although if it was on the shower I would think twice about doing it since we have a minimally sized tankless water heater. – Jim Stewart Nov 15 '17 at 14:07
  • Another feature of laundry sinks is that they generally don't have an overflow drain. I personally think the lack of an overflow is a defect. Perhaps the idea is that a laundry sink will be in a room with a floor drain, but this is normally not the case. One can install an external overflow in a sink in which a hole can be made, but this is some trouble. If I were installing a laundry sink I would consider looking for one with an overflow. Kitchen sinks likewise don't have an overflow. What is the thinking? I have see water overflows occur with this arrangement! – Jim Stewart Nov 15 '17 at 16:31
  • Hi Jim. This particular laundry room actually does have a floor drain and we've gone with just plain old cement floors - purchased from 20+ year smokers - for the adjoining rooms (with a plan of radiant floor heat and a thin layer of stained concrete over that next summer), so overflow is def. not a huge worry. – Jennifer Nov 16 '17 at 4:18
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You will be fine to tap the shower supply line there is no code issues doing this. The only problem may be and you have noted this is someone using the sink and shower at the same time. Its the same scenario as when someone flushes a toilet while the shower is in use there may be a change in water temp depending on the type of shower valve and supply line size.

  • Thanks so much! I just wanted to make sure. Logically it all worked out, but I didn't to do something like I was planning and have to tear open the wall later (and again) to take the supply further upstream for a more "correct" way of getting the desired sink actually in the laundry room. This will be a huge improvement over filling the mop bucket from the shower! – Jennifer Nov 16 '17 at 4:20
  • How many types of shower valves are there? The kind that divert to either tub or shower and just shower? Are there others (she asks simply out of curiosity) – Jennifer Nov 16 '17 at 4:26
  • Most newer shower valves are anti scald they regulate the temp so a pressure change prevents getting two much hot, there are many other kinds that will provide a specific temp and the older style that just mix the 2 supplies. – Ed Beal Nov 16 '17 at 14:06

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