Well Pump and Pressure Tank Reference for Water Treatment Service
Why this matters
Water treatment equipment installed on a well-water supply interacts with the well pump and pressure tank. When the pump cycles incorrectly, the treatment system suffers; when the pressure tank fails, the customer's water pressure drops and treatment effectiveness declines. A water treatment company that doesn't understand the well system creates installation problems and misdiagnoses service calls that are actually pump-side issues. This reference covers the basics of the well system from the water treatment company's perspective.
Well system components
A typical residential well has:
- Well casing: the vertical pipe from the well opening down to the aquifer
- Submersible pump (most common): the actual pump, located at the bottom of the well
- Drop pipe: the pipe from the pump up to the wellhead
- Wellhead: the cap at the top of the well
- Discharge pipe: from the wellhead to the home
- Pressure tank: typically in the basement or utility area
- Pressure switch: tells the pump when to turn on/off based on pressure
- Check valve: prevents water from flowing back down the well
Some wells (especially shallow wells) use a jet pump (in the home) rather than a submersible (in the well). The principles are the same.
How the system works
- Water flows out of a fixture; pressure drops in the system
- Pressure switch detects low pressure
- Pressure switch sends power to the pump
- Pump runs; water flows into the system AND into the pressure tank
- Pressure rises in the tank
- When pressure reaches the cut-off setpoint, switch turns pump off
- Tank holds water at high pressure; supplies fixtures during demand
- When pressure drops again, cycle repeats
The pressure tank acts as a reservoir that smooths the pump cycling.
Pressure switch settings
Standard residential settings:
- Cut-in pressure (pump starts): 30 PSI or 40 PSI
- Cut-off pressure (pump stops): 50 PSI or 60 PSI
These are paired:
- 30/50 (cut-in 30, cut-off 50) - older standard
- 40/60 (cut-in 40, cut-off 60) - modern standard
The cut-off pressure typically determines the home's "system pressure." A 40/60 system delivers water at pressures fluctuating between 40 PSI and 60 PSI.
Pressure tank function and sizing
The pressure tank's job:
- Stores water at high pressure between pump cycles
- Reduces pump short-cycling (pump running for brief periods)
- Maintains pressure during light usage
Sizing
Pressure tanks come in many sizes:
| Tank size (gallons) | Drawdown (gallons) | Suitable for |
|---|---|---|
| 20 gallon | 5-6 gallons | Small home, light demand |
| 36 gallon | 10-12 gallons | Standard residential |
| 86 gallon | 26-28 gallons | Larger home, irrigation demand |
| 119 gallon | 36-40 gallons | Heavy demand |
| 219 gallon | 65-72 gallons | Very heavy demand |
"Drawdown" is the water available between cut-on and cut-off pressures. Bigger tanks = more drawdown = less frequent pump cycling.
Pre-charge pressure
The pressure tank has an air pre-charge:
- Set 2 PSI below the cut-in pressure (e.g., 28 PSI for a 30/50 system; 38 PSI for a 40/60 system)
- Pre-charge is air pressure in the upper part of the tank (separated by a diaphragm)
- The pre-charge ensures the tank delivers water to the system without the pump running
Pressure tank failure modes
| Symptom | Likely cause |
|---|---|
| Pump short-cycles (turns on/off rapidly) | Diaphragm failed, pre-charge lost |
| Water hammer when pump starts | Diaphragm fails, water + air mixed |
| Pump runs frequently with light water use | Pressure tank not holding pressure |
| Visible water at the air valve | Diaphragm ruptured |
Pressure tanks have a service life of 5-15 years depending on water quality + maintenance. Replacement when failed is straightforward (drain the system, swap the tank, restore pre-charge).
Pump issues that affect water treatment
Pump short-cycling
The pump rapidly turning on and off:
- Cause: pressure tank failure OR severely undersized tank
- Effect on treatment: pressure surges damage softener valves, RO membranes, iron filter media
- Resolution: replace pressure tank
Pump unable to maintain pressure
Pump runs continuously but pressure stays low:
- Cause: pump failing, leak in drop pipe, leak in discharge pipe, water table dropping
- Effect on treatment: low pressure reduces softener regeneration effectiveness, RO production drops, UV may not get adequate flow
- Resolution: investigate pump system; may require pump replacement OR well work
Inconsistent pump operation
Pump cycles inconsistently:
- Cause: pressure switch failure, electrical issue, intermittent leak
- Effect on treatment: similar to short-cycling
- Resolution: diagnose; replace failing components
Water treatment installation considerations
When installing treatment equipment on a well system:
Location relative to pressure tank
The standard order:
- Well pump (in well)
- Pressure tank
- Sediment pre-filter
- Treatment equipment (softener, iron filter, UV, etc.)
- Home distribution
Treatment equipment AFTER the pressure tank. The pressure tank smooths the flow; the treatment equipment receives stable pressure.
Bypass valves
For every treatment unit installed:
- Three-valve bypass for service
- Allows water to bypass the unit while it's being serviced
- Critical on a well system (no municipal alternative)
Drain provisions
For backwashing softeners, iron filters, RO units:
- Drain destination is critical
- Air gap required by code in some jurisdictions
- Sump pump pit or utility sink common
- Verify drain capacity (a softener regeneration can dump 50+ gallons in 15 minutes)
Power circuits
Some treatment equipment needs power:
- Softener (smaller demand)
- UV (constant on, GFCI compatible)
- Iron filter (controller + sometimes oxidation pump)
- RO (booster pump if installed)
A dedicated 20-amp circuit for treatment equipment is good practice; verify GFCI compatibility for each device.
Cycling and treatment effectiveness
The pump's cycling pattern affects treatment:
Iron filter (manganese greensand):
- Requires steady flow for backwashing
- Pump cycling during backwash can disrupt the cycle
- Schedule backwash when household demand is low (overnight)
Water softener regeneration:
- Requires steady flow during brine cycle
- Pump cycling during regeneration affects rinse effectiveness
- Schedule regeneration when household demand is low
UV disinfection:
- Flow rate matters for UV dose
- Pump cycling means flow rate varies
- Some systems include a flow sensor that adjusts; others don't
RO:
References
- NGWA (National Ground Water Association) well system standards
- ANSI / NSF 14 (Plastic Pipe - well plumbing standards)
- ANSI / ASME B1.20 (NPT threads - wellhead fittings)
- IRC (International Residential Code) Plumbing chapter
- State well-drilling regulations
- Manufacturer documentation (Pentair Goulds, Franklin Electric, etc.)
- Manuall internal: Well Water Testing, Iron and Manganese Treatment, Diagnose Hard Water