Low-yield well storage tank systems: how they work, sizing and cost

A low-yield well storage tank lets a well that produces water slowly still run a household, because the water is stored ahead of time. Instead of pumping straight from the well into a small pressure tank, a storage system lets the well fill a large tank over hours, and a second pump draws from that tank when the faucets open. This page explains how these systems work, how large the tank should be, what they cost and what to ask an installer.

How does a well storage tank system work?

Penn State Extension describes the setup this way: the well pump fills a nonpressurized storage reservoir, and a second pump, the pressure pump, draws from the reservoir to supply the house. The reservoir becomes the primary source of supply for the pressure pump. Penn State Extension: Using Low-Yielding Wells Trade guidance adds the controls: the well pump is switched by floats or sensors in the storage tank, one low to start and one high to stop, rather than by a pressure switch, and the booster pump feeds a pressure tank controlled by a pressure switch. National Driller: Booster Systems for Low-yield Wells, Part 1 [PSU-LOWYIELD source note] [ND-BOOSTER source note]

The reason this helps is peak demand. Household water use bunches into short periods, and a pressure tank alone holds little usable water: only about 20 percent of its capacity. A 1 GPM well supplies only about 120 gallons in a two-hour peak, far short of what a family needs at that moment, even though the same well can produce 1,440 gallons over a full day. Penn State Extension: Using Low-Yielding Wells Storage moves the well's slow, steady output into the hours when you actually use water. [PSU-LOWYIELD source note]

How big should the storage tank be?

Penn State Extension's rule of thumb is about 100 gallons of storage for every person in the home, so a family of five needs about 500 gallons, and ideally enough to meet a full day's water use. Penn State Extension: Using Low-Yielding Wells New York's health department publishes a table tied to well yield and home size. It recommends a long-term sustainable yield of at least 5 gpm where possible, and no added storage above that: NYSDOH: Individual Water Supply Wells Fact Sheet #2, Water Storage [PSU-LOWYIELD source note] [NYSDOH-STORAGE source note]

The two approaches give different answers because one is a minimum and the other aims for a full day's supply. Larger storage costs more but gives more margin in a dry season, when yields can fall. Your installer should size the tank from your tested yield; see well yield tests for what that test should include, and how many GPM a well should produce for household demand.

What does a storage tank system cost?

Penn State Extension gives $250 to $500 for a 300 to 500-gallon tank, and says a household intermediate storage system without a chlorinator generally costs less than $1,500, depending on labor. Penn State Extension: Using Low-Yielding Wells Big cisterns are a different scale of project. Angi lists these prices for a 5,000-gallon above-ground tank and for buried systems: Angi: How To Install and Build a Cistern for Your Home [PSU-LOWYIELD source note] [ANGI-CISTERN source note]

Get an itemized quote that separates the tank, booster pump, pressure tank, controls, plumbing, electrical work and any excavation, so you can compare it with the cost of deepening the well or drilling a new one.

Tank materials, placement and sanitation

Penn State Extension notes that most tanks are plastic or concrete and must be protected from freezing, either buried below the frost line or placed in a heated garage or basement. Penn State Extension: Using Low-Yielding Wells An Alberta government fact sheet on cisterns lists steel, concrete, fiberglass and polyethylene as acceptable materials and describes the openings a sanitary tank needs: an access point, a watertight lid, a fill port and a vented overflow covered with fine mesh. It also recommends keeping a chlorine residual in stored water. Government of Alberta: Maintaining Your Cistern That is Canadian guidance, so use it as general practice and follow your own state and local rules. [PSU-LOWYIELD source note] [AB-CISTERN source note]

Storage has a side benefit: Penn State Extension notes that it lengthens chlorine contact time where water is treated and lets oxidized iron settle. Keep the tank clean, sealed against insects and surface water, and on the inspection list with the rest of the system.

Protecting the pump

A storage system only works if the well pump never runs the well dry. Penn State Extension says the well pump's rated capacity should be slightly less than the well's yield, and that a low-water signal should override other controls and stop the pump. Penn State Extension: Using Low-Yielding Wells Trade guidance recommends a dry-well protection device on submersible pumps and puts it plainly: there is no sense in using a 10-gpm pump in a 3-gpm well. National Driller: Booster Systems for Slow Producing Wells, Part 2 For sizing both pumps, see what size well pump you need. [PSU-LOWYIELD source note] [ND-BOOSTER2 source note]

Questions to ask an installer

1. What is my well's tested yield, and when was it measured?
2. What tank size do you recommend, and how did you calculate it?
3. Where will the tank go, and how will it be protected from freezing and contamination?
4. What controls stop the well pump at low water, and what alarms tell me the tank is low?
5. What does the quote include: tank, booster pump, pressure tank, wiring, plumbing and any treatment?

If storage will not close the gap, compare the other options in low-yield well solutions, including rehabilitation, deepening and a replacement well.