A water supply well assessment tests whether a well, or a set of wells, can deliver the water a project needs over the long term without unacceptable effects on neighbouring wells or streams. In Ontario it supports Permit to Take Water applications for larger supplies, and MECP Guideline D-5-5 assessments for developments on private wells. The pumping test design, analysis and report are completed by a licensed hydrogeologist (P.Geo.) or professional engineer (P.Eng.).
Which rules apply to your supply
The rules for a water supply well depend on its use and volume: wells for new homes on private services follow D-5-5, larger takings over 50,000 L/day need a Permit to Take Water, and domestic or livestock use under 379,000 L/day is exempt, with conditions.
| Supply | Framework |
|---|---|
| Wells for new homes on private services | D-5-5: pumping tests of at least six hours, water quality against drinking water objectives |
| Farm, golf course, commercial or institutional supply over 50,000 L/day | Permit to Take Water, usually Category 3 with a hydrogeological study |
| Communal supply for several lots | Permit to Take Water when the taking exceeds 50,000 L/day; confirm the drinking water system approvals with the municipality and the ministry early |
| Domestic or livestock use under 379,000 L/day | Exempt from a water taking permission (conditions apply) |
How the pumping test (well yield test) is run
A pumping test for a Permit to Take Water normally runs at least 24 hours at or above the requested rate, while a D-5-5 test for a private-well development runs at least six hours at a fixed rate.
For permit applications, the ministry's Category 3 guidance sets the expectations:
- Duration. Normally at least 24 hours; a 72-hour test is generally recommended. It can be shorter if the qualified person is satisfied the system is characterized.
- Rate. A step test first to find the right constant rate, then a constant-rate test at or above the rate requested in the application.
- Multiple wells. If wells will be pumped together under the permit, they are tested together to capture combined effects.
- Water levels. Continuous logging at one-minute intervals or less, especially early in the test, and recovery monitoring typically to 95%.
- Discharge. Pumped water routed so it does not recharge the aquifer being tested or cause erosion.
For private-well developments, D-5-5 sets a minimum six-hour continuous test at a fixed rate based on 3.75 L/min per person, never below 13.7 L/min, with recovery to 95% or 24 hours.
Interference and the well survey
The well survey finds who else draws from the aquifer, and the predicted drawdown at those wells and at nearby streams and wetlands sets the monitoring plan and contingency measures that go into the permit.
The study has to show who else draws from the aquifer. The Category 3 guidance asks for a reasonable effort to field-verify wells within the study area or 500 m of the pumping well, whichever is less, and beyond that any drilled wells where more than 1 m of drawdown is predicted and dug or bored wells where more than 0.25 m is predicted. Reasonable effort includes at least one daytime visit and one evening visit where no one answered the first time.
Predicted drawdown at those wells, and the effect on streams and wetlands, then sets the monitoring plan and the contingency measures that go into the permit.
Pumping test and well assessment cost
A pumping test and well assessment costs more as the test runs longer and more wells are pumped together, from one well with a 24-hour test up to a communal supply with three or more wells and a 72-hour test.
Use, test length and number of wells are the main inputs. Drilling new wells is billed separately by the well contractor.
| Answer | Indicative range |
|---|---|
| Starting point (Agricultural or irrigation, 6 hours, 1 well) | $7,000 – $11,000 |
| Water use | |
| Agricultural or irrigation (starting point) | $7,000 – $11,000 |
| Single commercial or institutional | $8,000 – $12,000 |
| Communal (multi-lot) | $14,500 – $21,500 |
| Pumping test duration | |
| 6 hours (starting point) | $7,000 – $11,000 |
| 24 hours | $10,000 – $15,000 |
| 72 hours | $14,500 – $21,500 |
| Number of wells | |
| 1 well (starting point) | $7,000 – $11,000 |
| 2 wells | $11,000 – $16,000 |
| 3 or more wells | $14,500 – $21,500 |
| Full span across all answers | $7,000 – $86,500 |
Each row changes one answer and leaves the others at the starting point. Indicative ranges, rounded to the nearest $500. They exclude well drilling, government application fees and HST. Final scope is confirmed by the hydrogeologist after reviewing your site.
You receive
A water supply well assessment delivers the pumping test analysis, water quality results, a well survey with predicted interference, the sustainable yield and recommended pumping rates, and any monitoring and contingency plan the permit needs.
- Pumping test data, graphs and analysis of aquifer properties
- Water quality results and their comparison with the applicable standards
- Well survey summary and predicted interference
- Sustainable yield and recommended pumping rates
- Monitoring and contingency plan for the permit, where one is needed
Have ready
Before the pumping test is scheduled, have the water demand, well records for existing wells, a site plan showing wells, buildings, septic systems and watercourses, and a place to discharge test water away from the well.
- The water demand: peak rate, hours per day, days per year
- Well records and construction details for existing wells
- A site plan with wells, buildings, septic systems and watercourses
- A place to discharge test water away from the well
What derails a test
A pumping test is most often derailed by a pump that stops mid-test, a rate that drifts, discharge too close to the well, or turbid water from a well that was not fully developed first.
- Pump stops mid-test. D-5-5 calls for continuous pumping with no stoppages; a failed generator means starting again.
- Rate drifts. Without a calibrated flow meter and regular checks, the analysis is unreliable.
- Discharge too close to the well, artificially recharging the aquifer.
- Turbid water at sampling time because the well was not fully developed first.
Worked cost examples
Each example runs the estimator's own calculation on a realistic set of answers.
-
One well for a commercial building, 24-hour test$11,000 – $17,000
Water use: Single commercial or institutional · Pumping test duration: 24 hours · Number of wells: 1 well
A single well and the ministry's normal minimum test length for a permit study. The 24-hour test adds field time and monitoring over the six-hour base.
-
Two irrigation wells for a farm, 72-hour test$21,500 – $32,500
Water use: Agricultural or irrigation · Pumping test duration: 72 hours · Number of wells: 2 wells
The recommended 72-hour test and two wells pumped together to capture combined drawdown. Agricultural use sits slightly below commercial in the estimator.
-
Communal supply, three or more wells, 72-hour test$57,500 – $86,500
Water use: Communal (multi-lot) · Pumping test duration: 72 hours · Number of wells: 3 or more wells
The largest case: several wells, a long test, a wide well survey and drinking water quality analysis for a supply serving many homes.
What the reviewer checks
A reviewer of a water supply well assessment checks the test rate and duration, the observation wells and water level data, the well survey, aquifer parameters, predicted interference, water quality and the monitoring plans.
- Test rate at or above the rate requested, after a step test
- Test duration, and why it is enough to show boundary effects
- Observation wells in the same formation, georeferenced and tied to a common datum
- Continuous water level data, especially early in the test, and recovery to about 95%
- Well survey effort and results
- Aquifer parameters (transmissivity, storativity) and the method used
- Predicted interference at representative wells and effects on surface water
- Water quality results against the applicable standards
- Monitoring and contingency plans that match the predictions
D-5-5 pumping test or Permit to Take Water pumping test?
The two pumping tests serve different reviews: a D-5-5 test supports a development on private wells and is often reviewed by the municipality, while a Permit to Take Water Category 3 test supports a larger taking reviewed by MECP.
| Aspect | D-5-5 (private wells) | PTTW Category 3 |
|---|---|---|
| Purpose | Show each future house well will have enough safe water | Show a larger taking will not cause unacceptable interference |
| Minimum length | Six hours continuous at a fixed rate | Normally at least 24 hours; 72 recommended |
| Rate | 3.75 L/min per person, not below 13.7 L/min | At or above the rate requested in the application |
| Recovery | To 95% or 24 hours, whichever is less | Typically to 95% |
| Reviewed by | Municipality or its reviewer, often | MECP |
An existing permit does not always need a new test when it comes up for renewal; our guide to PTTW renewal sets out the Category 1 test and the record a holder keeps.
Where this study is commonly required
Location pages with local requirements, groundwater data and the agencies involved, by region:
Greater Toronto and Hamilton Area
Central Ontario
Eastern Ontario
Southwestern Ontario
Water supply questions
Do I need a permit for the pumping test itself?
Not below 50,000 L/day: above that, a pumping test of no more than 7 days within a 30-day period, taking no more than 5,000,000 L/day, is registered on the EASR. Longer or larger tests need a Permit to Take Water.
How do I know whether my supply needs a Permit to Take Water?
If it will take more than 50,000 litres per day and is not exempt, it does. Water for domestic use or for watering livestock is exempt below 379,000 L/day. Try the decision tool with your expected daily volume.
Why does the test need observation wells?
A pumping well on its own tells you about the well, not the aquifer. Observation wells screened in the same formation show how far drawdown spreads, which is what the interference assessment needs. The ministry's Category 3 guidance asks for observation wells sited to characterize local conditions and possible off-site interference.
What if a neighbour says our well dried up theirs?
Baseline data is the answer when a neighbour says your well dried up theirs. A well survey before pumping, and monitoring during the test, show what the neighbour's well was doing before and during the taking. EASR water taking reports must include contingency measures for affected water users, such as supplying equivalent water, and permits carry conditions to prevent interference.
How many test wells does a rural subdivision need?
A rural subdivision needs at least three test wells for sites up to 15 hectares, four for 15 to 25 hectares and five for 25 to 40 hectares. D-5-5 sets these minimums and adds one more for each additional 20 hectares, with up to one per lot where supply is marginal.
Does the water quality analysis cover everything?
The water quality analysis does not cover everything: it covers the physical, chemical and bacteriological parameters the guideline or permit requires, plus anything the land use review suggests. That can include parameters linked to nearby farming, road salt storage or old waste sites within 500 m.
How does a D-5-5 pumping test differ from a Permit to Take Water pumping test?
A D-5-5 pumping test shows each future house well will have enough safe water, with at least six hours of continuous pumping at a fixed rate. A Permit to Take Water Category 3 test shows a larger taking will not cause unacceptable interference; it normally runs at least 24 hours, with 72 recommended, and is reviewed by MECP.
What happens if a water supply well assessment is not done?
Without a water supply well assessment there is no evidence that the well can deliver the water a project needs without unacceptable effects on neighbouring wells or streams. A farm, golf course, commercial or institutional supply over 50,000 L/day usually needs a Category 3 Permit to Take Water with a hydrogeological study, and D-5-5 sets minimum pumping tests for wells for new homes on private services.
Related studies
- Permit to Take Water & EASR
Work out whether a water taking needs an EASR registration or a Permit to Take Water.
- Severance Hydrogeological Study (D-5-4 / D-5-5)
Groundwater quality and well supply assessments for rural lot creation under MECP guidelines D-5-4 and D-5-5.
- Groundwater Monitoring & Annual Reporting
Water level and water quality monitoring programs, baseline private well surveys and annual reports.
- Hydrogeological study cost guide
Ranges for every study type, side by side.
Sources
- D-5-5 Private wells: water supply assessment (opens in a new tab), Government of Ontario (MECP).
- Permits to take water: application requirements (opens in a new tab), Government of Ontario (MECP).
- Technical guidance document for hydrogeological studies in support of Category 3 applications (opens in a new tab), Government of Ontario (MECP).
- Environmental permissions for water taking (opens in a new tab), Government of Ontario (MECP).