I'm planning to put an ADU (accessory dwelling unit) studio apartment over my garage to use as an office / spare bedroom. The garage is about 50ft from the house, and my house is on a well system with a pressure tank in the basement of the house.

I'm unsure what I need to do to run water to the ADU-- does it need its own pressure tank setup, and if so, how does that work with the well pump pressure switch? I can't imagine the house pressure tank would be able to push water that far with any kind of pressure.

Thanks for any advice.

  • Without a separate pressure tank, I’d be careful when I took a shower in the ADU when they’re doing laundry in the main house.
    – Lee Sam
    Apr 8, 2021 at 6:34
  • @LeeSam I wouldn't worry about laundry, washing machines only draw water for a short time. I'd be more worried about 3 people taking showers at the same time! So much of this stuff depends upon pump size and well production. Apr 8, 2021 at 10:24
  • @GeorgeAnderson I wasn’t so concerned about “quantity” of water as “quality”...particularly steady hot water in the shower. Changing a portion of the flow of the water can be scalding in the shower.
    – Lee Sam
    Apr 9, 2021 at 1:49

1 Answer 1


No, you don't need a separate pressure tank. Assuming you are on level ground, getting to a 2nd floor ADU would be about a 10' (?) vertical rise. Water pressure caused by gravity is .43 PSI per foot, so if level land and 2nd floor, you'd loose 4.3 PSI in pressure. Which would be roughly the same as between the first and second floor of a house. Flow rate is determined by several things, most notable pipe size....and in your case, pump size and how much the well can produce.

If you are very concerned about this, bigger is better...for an ADU 3/4" pipe would be fine, but 1" would be better.

Also, most pressure switches that control pumps are adjustable meaning you could set it a bit higher to make up for the 4 PSI, but I doubt you'd need to. Not knowing your specific setup, I can't be sure if it's adjustable or not, but most are.

  • so you're thinking I'd be good plumbing out from the original tank, running the 50' to the ADU and letting the house and ADU use the same system?
    – user101289
    Apr 8, 2021 at 13:24
  • Yes, you only have one well and one pump. Adding a second pressure tank wouldn't do anything to increase capacity, only add storage. I run two fairly large homes on one well going thru the same water softening system. Running 50' of pipe really is a nothing burger. As I've said many times here before, well systems all have their own characteristics, mostly production rate (how much water can be pumped from the well at what rate before you are "sucking air"?) and pump capacity. Unless you sub-let the ADU and your all taking showers at the same time, you should be fine. Apr 8, 2021 at 17:27

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