Ask ten districts how often they test their wells and you will get ten answers, and almost all of them will be a calendar: every well, every year, or every two years because that is how often the utility’s pump-test program will pay for it. The calendar is easy to budget and easy to defend. It is also the wrong way round.
A well that is losing 1% of its capacity a year can go two years between tests and nothing will be missed. A well losing 10% a year can cross the line from “rehabilitate soon” to “rehabilitate now, and it will not all come back” between one annual test and the next. Same calendar, completely different risk.
The interval should come from the well. This note gives a rule for setting it, a practical schedule, and what each kind of test is actually for.
Not all tests are the same test
Four different measurements get called “testing the well”, and they answer different questions at very different prices.
| Test | Who does it | What it answers | Cost |
|---|---|---|---|
| Water level check: static and pumping level with a meter reading | Your operator, about 20 minutes | Is specific capacity holding? | Almost nothing |
| Pump efficiency test: flow, head, input power | A test contractor or a utility program | Is the pump still on its curve, and what is the energy costing? | Modest |
| Step-drawdown test | A consultant or contractor | How much of the drawdown is the well and how much is the aquifer? | Moderate |
| Downhole video survey | A contractor, pump pulled | What does the screen actually look like? | Highest — the pump has to come out |
The first one does most of the work. Specific capacity — flow divided by drawdown — is the earliest honest sign that a well is plugging, it needs nothing but a sounder and a flow meter, and your own staff can take it. The others are for confirming what it shows, and for the pump.
The rule: at least four readings before it can cross the line
Every well has a trigger — the specific capacity decline, measured from its baseline, at which the district will rehabilitate. Common practice puts it somewhere between 15% and 25%. Every well also has a remaining margin: how far it is today from that trigger. And every well with a history has a decline rate: how fast its specific capacity has been falling, in percent per year.
Put them together and the interval writes itself. You want to see the well at least four times before it could reach the trigger, so that the trend is visible and the decision is planned rather than discovered:
test interval (years) ≤ remaining margin ÷ (decline rate × 4)
Three wells, one rule:
| Well | Margin to its trigger | Decline rate | The rule gives | Schedule |
|---|---|---|---|---|
| A | 20% (5% down, trigger 25%) | 1% a year | 5 years | Every 6 months, the floor |
| B | 10% (10% down, trigger 20%) | 6% a year | 5 months | Quarterly |
| C | 6% (14% down, trigger 20%) | 8% a year | 2.25 months | Monthly |
Two limits keep the rule honest. A floor: no well goes longer than six months without a water level check, whatever the rule says, because a stable well can change quickly — a pump problem, a neighbor’s new well, a dry year. And a ceiling on effort: monthly is plenty for a well-level check. If a well needs watching more often than that, it needs a decision, not more data.
For a well with no history yet, start quarterly. After two years there are eight readings and a real decline rate to work from.
Why the readings have to be comparable
A schedule is worthless if the readings cannot be compared. Specific capacity depends on how hard the well is pumped and for how long, so every check needs:
- The same rate, or close to it. Pump a well harder and its specific capacity drops even when it is clean. Where the rate has to differ, write it down and compare against a baseline at a similar rate.
- The same pumping time before the reading. The pumping level keeps falling for hours after start-up. Pick a time — after four hours of running, say — and use it every time.
- A real flow, from the meter, not the design rate on the plans.
- The season. Static levels follow the aquifer’s annual cycle. Comparing August to August is fairer than August to February.
The Water Replenishment District of Southern California’s guidance on specific capacity makes the same point: the same pumping time frame should be used for every test, so each can be compared fairly with the first one.
A practical schedule
For a municipal production well, this is a sensible default, tightened by the rule above where the well is declining:
- Continuously, if you have SCADA: flow, run hours, amps or kW, and pumping level if the well has a transducer. See our note on scheduling pumps around time-of-use rates for what the flow and hours are good for.
- Monthly to every six months, by the rule: a static and pumping level check with a meter reading. Record specific capacity and plot it against the baseline.
- Every one to two years: a pump efficiency test. The well-level checks tell you about the well; this tells you about the pump and what its energy is costing. In PG&E territory, the Advanced Pumping Efficiency Program subsidizes one test per pump in any 23-month period, and a test needs a proper flow meter section to be valid.
- After any rehabilitation or pump change: a new baseline test, ideally a step-drawdown test. Every comparison after that is against the new baseline, not the old one.
- When specific capacity has fallen 10% to 15%, or every five years: a downhole video survey, timed with a pump pull where possible so the rig is only mobilized once.
What the readings buy you
The point of all this is not the data. It is the decision. A well watched on its own schedule gets rehabilitated at the right time — before scale that has sat on the screen for years hardens and stops responding to treatment, and before the lost capacity shows up as a failed summer — and it gets rehabilitated in the budget year it was planned for, not the one it forced. See when to rehabilitate a water well for what waiting costs, and how to tell the pump, the well and the aquifer apart when the readings start to move.
What to do with this on Monday
- Find each well’s baseline specific capacity and the rate and pumping time it was measured at.
- Work out each well’s decline rate from the tests you already have. Two tests a few years apart are enough for a first estimate.
- Set each well’s interval with the rule, floored at six months.
- Write the test conditions down — rate, pumping time, season — so every future reading is taken the same way.
- Put the checks on the operators’ schedule, not the consultant’s. Twenty minutes with a sounder is the cheapest engineering a district will ever buy.
Quick answers
How often should a municipal well be tested?
Take a static and pumping water level with a meter reading at least every six months, and more often on a well that is declining — often enough to see it at least four times before it could reach the rehabilitation trigger. Test pump efficiency every one to two years.
What is the cheapest way to monitor a well’s condition?
Specific capacity: flow from the meter divided by the drawdown from a sounder reading. It takes an operator about twenty minutes and is the earliest reliable sign of screen and gravel-pack plugging.
When should a well get a video survey?
When specific capacity has fallen 10% to 15% from baseline, or about every five years on a stable well — ideally timed with a pump pull so the rig only comes out once.
See each of your wells’ decline rate and the test schedule it implies. Request a walkthrough →
Sources
- Water Replenishment District of Southern California. Specific Capacity — A Measure of Well Performance, Well Problems, and Aquifer Transmissivity, Technical Bulletin TB02. Source for using the same pumping time frame in every test so each compares with the first, and for a 25% decline as a rehabilitation trigger.
- Southeast Hydrogeology. Using Specific Capacity to Monitor Well Performance. Source for a 15% decline as a rehabilitation trigger and for the same continuous pumping time frame in every test.
- Advanced Pumping Efficiency Program, Center for Irrigation Technology, California State University, Fresno. How to Get a Pump Test, Eligibility and Technical Advisory (July 2014). Source for one subsidized test per pump in a 23-month period; the test section a valid flow reading needs, eight to ten pipe diameters of straight pipe upstream and two to four downstream; and eligibility for non-residential PG&E electric and natural gas accounts.
Every link above was retrieved and read on 2026-09-26; the Advanced Pumping Efficiency Program links were replaced and read on 2026-09-30, after the program moved its pages to pumpefficiency.org. Paid standards are named by designation so you can check them against your own copy.