Understanding Oshawa's water
Oshawa's water comes from Lake Ontario through the Oshawa Water Supply Plant, the largest plant in the connected Oshawa/Whitby/Ajax system. Its approved capacity is 134,000 cubic metres a day.
Durham doesn't publish a hardness figure, but Lake Ontario water measured elsewhere in the GTA runs 119 to 130 mg/L (about 7 to 7.6 grains per gallon), which is hard. Expect similar water here, and confirm it with a free in-home test.
What the 2025 report shows
- Fluoride: added (0.15 to 0.77 mg/L at the Oshawa plant in 2025)
- Free chlorine in the pipes: 0.30 to 3.60 mg/L
- Sodium: 14 to 24.3 mg/L
- Lead: 106 plumbing samples ranged from non-detect to 0.0032 mg/L in 2025, under the 0.01 mg/L limit
Source: Region of Durham, Oshawa/Whitby/Ajax Drinking Water System 2025 Annual Report.
Why Oshawa homes treat their water
Oshawa has a lot of older housing near the downtown and lakeshore. Older plumbing is where sediment, scale and, in rare pre-1950s homes, lead pipes show up.
Recommended water treatment for Oshawa homes
We recommend systems based on where your water comes from. Your free in-home test confirms the fit before anything is installed.
Oshawa homes on municipal water
Downtown Oshawa, Lakeview, Eastdale, Donevan, Centennial, Kedron, Windfields, Taunton, Samac, Northglen
Softening for scale, carbon filtration for chlorine taste and smell, and reverse osmosis for drinking water. The Enhanced Water Softener handles the first two in one tank.
Homes on private wells
Raglan, Columbus and the rural north of Oshawa
Private wells need their own plan: iron and manganese removal, softening, tannin treatment if the water is tea-coloured, and UV disinfection for bacteria.
Iron & Manganese Filter
Birm media removes iron, manganese and the orange or black stains they leave.
See Iron & Manganese Filter
SoftBlu Water Softener
High-capacity softener that stops scale on fixtures, kettles and appliances.
See SoftBlu Water Softener
UV Pro
Ultraviolet disinfection for well water: bacteria, viruses and cysts.
See UV Pro
Tannin Eliminator
Clears tea-coloured water and yellow stains caused by tannins.
See Tannin EliminatorPopular in Oshawa
Nearby areas we also serve
Questions
How hard is Oshawa water?
Durham Region doesn't publish a hardness figure for Oshawa. Lake Ontario water elsewhere in the GTA measures 119 to 130 mg/L, which is hard. Our free in-home test measures your tap.
Does Oshawa add fluoride to the water?
Yes. Durham's 2025 report shows fluoride added (0.15 to 0.77 mg/L at the Oshawa plant in 2025).
Is there free well water testing in Oshawa?
Yes. Durham Region Health Department tests private well water for bacteria for free. Pick up a bottle at a Region service location. Our in-home test covers iron, hardness and other minerals.
Free in-home water test
Find out what's in your Oshawa water
We test your water at your home, show you what's in it, and recommend the system that fits.
- Free
- About 30 minutes
- No obligation