Off-Grid Water: Wells, Rainwater and Treatment

A reliable water supply is the first system to get right on any off-grid property. This guide covers how much water a household actually uses, the main sources available in Canada and the northern United States, how to size rainwater storage with real numbers, how to pump and treat water, what to test for, and how to protect the whole system from freezing.

How much water you need

Urban Canadian households use roughly 200 to 250 L (53 to 66 US gal) per person per day, mostly for toilets, showers and laundry. Off-grid households with low-flow fixtures and careful habits commonly use 50 to 100 L (13 to 26 US gal). Drinking and cooking need only 3 to 5 L per person per day, but that water must be of the highest quality.

Water sources

Drilled wells

A drilled well is a narrow borehole, usually lined with 150 mm (6 in) steel casing, reaching an aquifer 30 to 150 m (100 to 500 ft) down. Sealed at the surface and drawing from depth, a properly built drilled well is the best-protected source available. Yield is measured by pump test. A well producing 4 L/min (about 1 US gal/min) continuously supplies 5,760 L per day, enough for a household if storage covers peak demand.

Dug wells

A dug well is a wide, shallow hole, often 0.9 to 1.2 m (3 to 4 ft) across and under 10 m (33 ft) deep, lined with concrete rings. Shallow groundwater is exposed to runoff, septic effluent, manure and seasonal drying. Dug wells need a watertight raised cover and ground graded away from the well, and should be tested more often than drilled wells.

Springs

A spring is groundwater that surfaces on its own. Collect it in a spring box, a sealed chamber that captures water below ground before it is exposed to animals or runoff. Ditch surface water around the box and fence out livestock. Flow often drops sharply in late summer, so measure it in August or September before relying on it.

Surface water

Lakes, creeks and ponds must always be treated before drinking. Even clear mountain water can carry Giardia, Cryptosporidium and bacteria from wildlife. Set intakes off the bottom and below the surface, protected from ice.

Rainwater

Roof rainwater is free of groundwater contaminants such as arsenic, but it picks up bird droppings, leaves, dust and anything leaching from the roofing. Treat it as non-potable until filtered and disinfected.

Rainwater collection maths

The basic relationship is simple: 1 mm of rain falling on 1 m² of surface produces 1 L of water. In imperial terms, 1 in of rain on 1 sq ft produces about 0.62 US gal.

Use the roof's horizontal footprint, not the sloped area; a steep roof and a flat roof over the same floor plan catch the same rain. Then apply a collection efficiency for evaporation, splash, overflow and first-flush losses. Use 0.8 (80%) for a metal roof with good gutters, and less for asphalt shingles or rough surfaces.

Collected volume (L) = roof footprint (m²) × rainfall (mm) × efficiency

Cistern size is set by the longest dry period you must get through, not by annual rainfall. On the BC coast and in the Pacific Northwest, summers are dry. On the Prairies, the dry season is winter, when snow sits on the roof.

First-flush diverters

The first rain after a dry spell washes the dirtiest material off the roof. A first-flush diverter is a pipe or chamber that fills with this runoff before cleaner water passes to the tank. A slow-drip outlet empties it between storms.

A common rule of thumb is to divert 0.5 L per square metre of roof (about 1.2 US gal per 100 sq ft). For the 120 m² roof above, that is 120 × 0.5 = 60 L. A 100 mm (4 in) pipe holds about 8.1 L per metre (0.65 US gal per foot), so 60 L needs about 7.4 m (24 ft) of pipe; a wider chamber or small drum is more practical. Add gutter leaf screens and a fine screen at the tank inlet.

Storage tanks and freezing protection

Cisterns are made of polyethylene, fibreglass, concrete or lined steel. A drinking-water cistern must be opaque to stop algae, sealed against insects and animals, and fitted with a screened overflow and a lockable hatch. Draw water from above the bottom, ideally with a floating intake, so settled sediment stays put.

Freezing is the main threat to storage in most of Canada. The options are:

• Bury the tank and piping below local frost depth, which ranges from under 0.5 m (1.6 ft) on the BC south coast to over 2 m (6.6 ft) on the Prairies. Use only tanks rated for burial.
• Keep the tank indoors in a heated space, on a floor that can carry it: a 2,000 L tank weighs 2 tonnes.
• Insulate an above-ground tank and heat it, which only works with reliable winter power.
• Use the tank seasonally and drain it before freeze-up.

Supply lines must also run below frost depth or be insulated and heat-traced. A pitless adapter lets the well line leave the casing below ground.

Pumps and pressure tanks

Submersible pumps

A submersible pump sits in the casing below the water level and pushes water up. It is standard for drilled wells. Most run on 120 V or 240 V AC and draw 700 to 2,000 W running, with a higher starting surge; check that your inverter can supply it.

Jet pumps

A jet pump sits above ground and lifts water by suction. The theoretical limit is about 10.3 m (34 ft) at sea level; the practical limit is about 7.5 m (25 ft) from pump to water surface, and less at higher elevations. Jet pumps suit dug wells, cisterns and lakes.

12 V and 24 V DC pumps

Low-voltage DC pumps run directly from batteries or solar panels. A 24 V submersible drawing 4 A uses 96 W; delivering 200 L at 10 L/min takes 20 minutes, or 32 Wh per day. DC pumps suit slowly filling a cistern during daylight, and surface DC pumps can pressurize a cabin from a tank.

Pressure tanks

A pressure tank holds an air cushion behind a diaphragm or bladder, storing pressurized water so the pump does not start every time a tap opens. A pressure switch starts the pump at cut-in and stops it at cut-out. Common settings are 30/50 psi (207/345 kPa) and 40/60 psi (276/414 kPa). With the tank empty of water, set the air precharge 2 psi (14 kPa) below cut-in: 28 psi (193 kPa) for a 30/50 switch, or 38 psi (262 kPa) for a 40/60 switch.

The usable volume between cut-out and cut-in, called drawdown, is about 30% of total tank volume at 30/50 psi and about 26% at 40/60 psi when correctly precharged.

Treatment

Treat in stages, each protecting the next: particles first, then taste and chemical contaminants, then disinfection.

Sediment filtration

A sediment cartridge removes sand, silt and rust; a common setup is 20 or 25 micron followed by 5 micron. Gauges on each side of the housing show when pressure drop calls for a change.

Activated carbon

Carbon filters reduce chlorine, many organic chemicals, and bad tastes and odours. They do not disinfect, and a carbon filter left unused in warm conditions can grow bacteria. Replace on schedule.

Ultraviolet (UV) disinfection

A UV lamp inactivates bacteria, viruses and protozoa, including Giardia and Cryptosporidium, without chemicals. It has two strict requirements.

• Clear water. Particles shade microbes, and iron, manganese and hardness coat the quartz sleeve. Typical limits are turbidity below 1 NTU, iron below 0.3 mg/L, manganese below 0.05 mg/L and hardness below about 120 mg/L (7 grains per gallon), with UV transmittance of at least 75%. Treat these first if a test shows them.
• Constant power. The lamp must run whenever water can flow. A 40 W unit running 24 hours uses 40 × 24 = 960 Wh per day, which is a significant load on a small solar system. If power fails, water passing through is untreated.

Choose a unit certified to NSF/ANSI Standard 55 Class A, which delivers a dose of at least 40 mJ/cm². Replace the lamp yearly (lamps lose output before they visibly dim) and clean the sleeve when you do.

Chlorination

Chlorine disinfects and leaves a residual that protects stored water. Continuous chlorination uses a metering pump and needs contact time. Shock chlorination is a one-time treatment after well work, flooding or a positive bacteria test.

Boiling

Boiling is the simplest emergency disinfection. Bring water to a rolling boil and keep it there for at least 1 minute. At elevations above about 2,000 m (6,500 ft), boil for 3 minutes. Boiling kills pathogens but does not remove chemicals such as arsenic, nitrate or fuel; it concentrates them slightly. For emergency chemical disinfection of clear water, add 2 drops of unscented 5–6% household bleach per litre, mix, and let it stand 30 minutes. Filter cloudy water first.

Testing

Private water supplies are the owner's responsibility. Health Canada and the US EPA publish limits used for comparison. Use an accredited laboratory and its sample bottles; health authorities often offer low-cost bacteria testing.

• Bacteria (total coliforms and E. coli): at least once a year, and ideally in spring and fall. Also test after flooding, a change in taste, colour or odour, or any work on the well. The guideline for both is zero per 100 mL.
• Full chemical analysis: when a well is new, when you buy a property, and every few years after that.

Some contaminants come from local geology and are common in parts of British Columbia, the Maritimes, Quebec, Saskatchewan and New England. They have no taste or smell; only a lab test finds them.

Winterizing

An unheated seasonal cabin must be drained completely. Water left in a low spot, pump housing or trap will freeze and split it.

1. Shut off power to the pump and water heater. Never drain an electric water heater with power on; the elements burn out in seconds.
2. Close the main supply valve and open every tap, hot and cold, including outdoor taps and shower valves.
3. Drain the pressure tank, the pump housing (jet pumps have a drain plug), filter housings and the UV chamber. Remove filter cartridges.
4. Drain the water heater through its drain valve, with a tap open to let air in.
5. Blow out the lines with compressed air at about 2.8 to 3.4 bar (40 to 50 psi).
6. Flush and sponge out toilets, then pour propylene glycol RV antifreeze into toilet bowls and every drain trap. Never use automotive (ethylene glycol) antifreeze, which is toxic.
7. Leave taps and drain valves open over winter, and label the system so nobody turns it on before it is reassembled.

For a system in winter use, keep the pump and pressure tank in a heated space, heat-trace pipes above frost depth, and fit a low-temperature alarm in the pump room.

Key points

• Plan for 50 to 100 L per person per day with conservation, and size storage for the longest dry period, not annual rainfall.
• Rainwater: 1 mm on 1 m² gives 1 L. Use the roof footprint and an efficiency of about 0.8.
• Drilled wells are the best-protected source. Treat all surface water and rainwater before drinking it.
• Set pressure tank precharge 2 psi below cut-in; usable drawdown is only 26 to 30% of tank volume.
• Treat in order: sediment, carbon, then disinfection. UV needs clear water and constant power.
• Test for bacteria at least once a year, and test for arsenic, uranium and manganese where geology makes them likely.
• Drain everything before freeze-up, and use only RV antifreeze in traps.

This guide is general information. Codes, permits and safety requirements vary by province, state and municipality. Check local rules and use a qualified professional for electrical, gas, chimney and septic work where required.

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