Capture
Roofs, pavement and compacted areas collect rainfall and can produce rapid runoff.
Understanding stormwater
Stormwater connects the roof, lot, street, sewer system and watershed.
Rain and snowmelt do not disappear at the property line. They move through roofs, downspouts, soil, driveways, swales, streets, pipes, creeks and receiving waters.
- Ontario-focused
- Plain-language guidance
- Risk reduction, not guarantees
The essential answer
Stormwater is rain or snowmelt that flows over land or built surfaces. Homeowner actions affect how quickly water leaves a property, where it goes and whether it creates risk for the building or neighbouring properties.
Who this guide supports
Use this page when the property, question or decision matches one of these situations.
- Homeowners who want to understand drainage before making changes
- Residents comparing downspout, grading or rain-garden options
- Property owners near creeks, valleys or low-lying streets
- People preparing questions for a contractor or municipality
Understand the system
Four parts of the decision deserve separate attention.
Convey
Gutters, downspouts, swales, ditches, curbs and pipes move water across and away from property.
Store and infiltrate
Soil, vegetation, rain gardens and storage features can slow or absorb water where site conditions allow.
Release
Water eventually reaches a sewer, ditch, creek, lake or groundwater system, subject to local design and regulation.
Guidance 1
Read the lot as part of a system
Observe where water begins, which surfaces shed it, where flows combine and where water leaves the property. A change that protects one area can create a problem elsewhere if discharge is redirected carelessly.
Neighbouring properties, easements, municipal rights-of-way and conservation constraints may affect what can be changed.
- Follow visible drainage routes after moderate rain
- Do not block a shared swale
- Keep outlets away from foundations where permitted
- Ask before directing water to a street or neighbouring lot
Guidance 2
Understand impervious surfaces
Roofs, driveways, patios and compacted soil reduce infiltration and can increase the speed and volume of runoff.
Renovations that add hard surface should include a drainage review, especially where the lot already has low points or limited outlet capacity.
- Review additions and widened driveways
- Protect permeable and landscaped areas
- Maintain eavestroughs and downspouts
- Consider local rules for disconnection and infiltration
Guidance 3
Connect property action to watershed resilience
Property-level action cannot replace municipal infrastructure, but thousands of properties influence peak flow, sewer loading and water quality.
RSM frames homeowner measures as one layer within a broader system that includes public infrastructure, land-use planning, maintenance, warning and emergency response.
- Use official local guidance
- Support maintenance of shared drainage features
- Avoid dumping pollutants into storm drains
- Learn local flood-warning sources
Practical workflow
Move from observation to a documented next step.
- 1
Observe roof, driveway and landscape runoff
- 2
Identify swales, drains, ditches and outlet points
- 3
Check municipal rules before altering drainage
- 4
Choose measures suited to soil, slope and available space
- 5
Inspect the system seasonally and after major storms
Homeowner checklist
Record each completed item and create a follow-up action for anything unresolved.
Continue through the RSM system
Related guidance, programmes and professional pathways.
Official source pathway
Use current public sources for emergency, insurance, programme and technical context.
RSM summarizes and connects information but does not replace the issuing authority. Review the current official page before acting.
Frequently asked questions
Clear limits help homeowners make better decisions.
Is stormwater the same as sewage?
No. Stormwater is rain or snowmelt runoff. Sewer systems and local arrangements vary, and some older areas may have combined infrastructure.
Can I send a downspout anywhere on my lot?
No. Discharge must respect building, drainage, neighbour and municipal requirements.
Does a rain garden prevent basement flooding?
It can help manage some runoff where appropriately designed, but it does not address every flood pathway.
Who controls the storm sewer?
Public sewer ownership and responsibilities vary. Municipalities manage public systems, while owners are responsible for many private-side components.
Editorial and review note
This educational page was prepared by Regional Stormwater Management using official public sources and a risk-reduction framework. It does not provide engineering, legal, insurance or municipal approval. Content is reviewed when official guidance changes and on the RSM editorial schedule.
Recommended next step
See how stormwater can reach a basement
Compare sewer backup, overland flow, groundwater and system-failure pathways.