Surface water is all water that stands or flows openly at the surface: ditches, brooks, canals, rivers, lakes, ponds and reservoirs. It is the counterpart of groundwater, which sits underground within the soil.
Surface water bodies are almost always managed water. Depending on the country and the watercourse, responsibility lies with a drainage board, water authority, environment agency or navigation authority.
Why it matters in construction
- Water level control. The level held in a watercourse influences the groundwater level nearby — and therefore whether a cellar stays dry and whether a timber pile foundation stays submerged.
- Rainwater disposal. For new build and new hard surfacing the rule is increasingly: do not send rainwater to the combined sewer, but infiltrate it or discharge it at a restricted rate to a watercourse.
- Attenuation. Anyone creating a large area of hard surfacing is usually required to provide compensating storage.
- Building next to water. Revetments, jetties, culverts and bridges intervene directly in the water system.
Rules to watch for
- Consent or permit. Work in, over, under or next to a watercourse usually requires consent from the relevant authority, or at minimum a notification. That covers a jetty, a culvert under a driveway, a bank revetment and infilling a ditch.
- Protected margin. A strip alongside a watercourse is subject to restrictions on building, storage and planting, measured from the top of the bank. The width differs per authority and per watercourse class — always check the local register and byelaws.
- Infilling is not casual. Filling or culverting a watercourse changes the water system and needs consent; lost storage generally has to be replaced elsewhere.
- Discharges. Discharging anything other than clean rainwater is subject to permit. Construction water containing cement residue is strongly alkaline and must not enter a watercourse.
Practical tip: check the authority’s register of watercourses before you design anything. It shows which ditch has what status, who is responsible for maintaining it and what margin applies. It is free to consult and it prevents expensive surprises.
Quantity and quality
Water management always balances two things at once: enough water in dry periods and enough room in wet ones. Water quality legislation adds requirements for chemical and ecological status. That is why naturalised banks, settlement facilities and the separation of foul and surface water keep appearing in modern designs.
Related terms
- Water table
- Infiltration
- Rainwater drainage
- Land drainage
- Sheet piling
Learn more about building terms in our knowledge base at fredsdiyplans.com.