Adding ADU/ALQ to existing well - where do I tap in?

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New Member
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WA State, King County
Bear with me, well-newb here ;)

We currently have a setup for our house with a well (130' deep) that we want to add a second ADU/ALQ building to. This new building will have fairly low water usage (single person, grandma takes quick showers). The questions are: where do we tap into the existing setup and do we need a separate pressure tank?

Current setup (10 years old):
1) well with pump
2) line to the house
3) utility water tap with backflow preventer valve
4) pressure tank with switch
5) house internals, water heater etc.

From a construction point of view, it would be easiest to tap in at 2). Tapping in after 4) would be quite challenging.
My thinking is: the existing pressure tank would be enough to provide adequate system pressure for a low-usage ADU/ALQ building, since the utility tap (at 3) has good pressure today.
- Where should I tap in?
- Do I have to (or should I) add a separate pressure tank in the ALQ/ADU building?

What do the pros think?

Thanks from the woods in the Cascades!


Cary Austin
Staff member
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Lubbock, Texas
Water comes from the well and pump, not the pressure tank. You didn't say what size pump and tank you have or how deep the well is? Only one pressure tank is needed and you can tap into the line just about anywhere, as long as there is no check valve above ground anywhere. When adding more demands to a pump, cycling on and off too much is the issue. Pump systems used to supply multiple dwellings either needs a larger pressure tank, or just add a Cycle Stop Valve.

CSV1A hydrant at well 20 gal tank 6 houses.jpg

Hey, wait a minute.

This is awkward, but...

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