Tiny House Water Systems: Off-Grid Collection & Filtration
How Much Water You Need
Start by tracking how much water you actually use. Most tiny house couples land between 40 and 80 gallons per day. Heavy users who shower longer, do laundry on-site, or run a flush toilet can hit 80 to 100 gallons.
Example daily use for a water-conscious couple:
- Drinking and cooking: 3 gallons
- Dishes: 5 gallons
- Showers (low-flow 1.5 GPM, 5 min each): 15 gallons
- Hand washing and cleaning: 5 gallons
- Misc (pets, plants, etc.): 5 gallons
Total: about 33 gallons per day
Add laundry (20 to 30 gallons per load) or a flush toilet (15 to 30 gallons per day) and daily use climbs fast. A composting toilet is one of the biggest water savers for off-grid living.
Low-flow fixtures make a real difference. A standard shower head uses 2.5 gallons per minute. A low-flow head uses 1.5 GPM or less. Faucet aerators drop sink flow to about 0.5 GPM. These changes can cut water use 30 to 50% with no real loss in comfort.
Three Water Sources
Rainwater — You collect runoff from your roof into storage tanks. Works well in areas with steady rainfall. Low running cost after install. You need enough roof area and storage to get through dry spells.
Well — You drill into the ground and pump water up. Gives steady supply year-round in most areas. Higher upfront cost. Needs electricity or solar to run the pump.
Spring — If you have a natural spring on uphill land, gravity can deliver water to your house with no pump. Rare, but ideal when available. You still need filtration and legal rights to the water.
Rainwater Collection Systems
Rainwater systems catch roof runoff, store it in tanks, and filter it before use. They work best where you get at least 20 inches of rain per year and have enough roof area.
Figure Out How Much You Can Collect
Use this formula: Roof area (sq ft) × annual rainfall (inches) × 0.623 × 0.85 = gallons per year
The 0.85 accounts for water lost to evaporation, overflow, and first-flush waste.
- Example: 400 sq ft roof, 40 inches of rain per year
- 400 × 40 × 0.623 × 0.85 = about 8,500 gallons per year
At 50 gallons per day, a couple uses about 18,250 gallons per year. That 400 sq ft roof in a 40-inch rain zone covers less than half your need — you would need a larger roof, more storage, strict conservation, or a backup source.
Example: Same roof in Portland, Oregon (about 43 inches of rain) 400 × 43 × 0.623 × 0.85 = about 9,100 gallons per year — still short for two people at 50 gal/day without conservation or backup.
Size Your Storage Tank
Store enough water to last through dry weeks. Target 2 to 4 weeks of supply.
Example: 50 gallons per day × 21 days = 1,050 gallons
Most tiny house couples install 500 to 1,000 gallon tanks. In dry climates, go bigger or plan a backup well or water delivery.
Set Up Collection and Storage
Gutters and downspouts — Use 5-inch gutters on a tiny house roof. Add leaf screens to keep debris out.
First-flush diverter — The first few gallons off a dry roof carry dust, pollen, and bird droppings. A diverter sends that dirty first runoff to a drain, then sends clean water to your tank. Costs $50 to $200 and improves water quality a lot.
Storage tanks — Plastic (poly) tanks cost $0.60 to $1.20 per gallon and work well for 500 to 2,500 gallons. Choose food-grade, UV-resistant models. Dark colors reduce algae growth. Above-ground tanks are easier to install and clean. Bury tanks only if you need freeze protection and have access for maintenance.
Overflow drain — Route overflow away from your foundation during heavy rain. Install a screen on the tank inlet to block insects and debris.
Wells and Springs
A well gives you groundwater that does not depend on rainfall. Once drilled, a good well can last decades. The main cost is upfront — drilling and the pump system.
Well Drilling
Drilling costs $15 to $50 per foot in most areas. Total depth depends on your local water table.
Shallow well (25 to 80 feet) — $3,000 to $8,000 total. Works where the water table is high. More risk of contamination and seasonal dry-up.
Deep well (100 to 300 feet) — $8,000 to $20,000 total. Better water quality and year-round flow in most regions. What most off-grid owners need in areas without a shallow aquifer.
You need a permit before drilling in almost every state. A licensed driller handles the work. The well gets cased with steel or PVC pipe and sealed to keep surface water out. Test the water before you drink it — bacteria, nitrates, and minerals vary by location.
Well Pump and Pressure
Submersible pump — Sits below water level in the well. Quiet and reliable. Costs $400 to $2,000 depending on depth and flow rate. Most tiny houses need 0.5 to 1 horsepower.
Jet pump — Sits above ground. Only works for shallow wells under 25 feet. Cheaper ($300 to $800) but noisy and needs freeze protection.
Pressure tank — A 20 to 40 gallon pressure tank ($150 to $500) stores pressurized water so the pump does not cycle on and off every time you open a faucet. Keeps pressure at 40 to 60 PSI like a normal house.
Solar well pump — Runs directly from solar panels or from your battery bank. Costs $800 to $3,000. Good for off-grid properties. Pair with a large storage tank so you have water when the sun is not out.
Springs
A spring on your property can feed your house by gravity if the spring sits uphill from your build site. You need at least 1 to 3 gallons per minute year-round. Build a small collection box at the spring source with a screened intake and overflow. Run buried pipe to a storage tank or directly to the house.
Check water rights before you develop a spring. Many western states treat spring water as a regulated resource even on private land.
Filtration and Safe Drinking Water
Never drink untreated water from a roof, well, or spring. Filtration and testing are not optional. Even clear water can carry bacteria, viruses, or chemicals you cannot see or taste.
Three-Stage System for Drinking Water
Stage 1: Sediment filter — Removes sand, rust, and debris. A whole-house sediment filter ($50 to $150) protects pumps and downstream filters. Replace cartridges every 3 to 6 months.
Stage 2: Carbon filter — Removes chlorine taste, many chemicals, and odors. Carbon block filters cost $100 to $400 for the housing plus $20 to $60 per replacement cartridge. Replace every 6 to 12 months.
Stage 3: UV sterilizer — Kills bacteria and viruses with ultraviolet light. UV units for tiny house flow rates (6 to 12 GPM) cost $400 to $900. Replace the UV lamp once a year ($80 to $150). Water must be clear for UV to work — sediment filter must come first.
A three-stage sediment + carbon + UV system costs $800 to $1,800 installed. Budget $150 to $300 per year for filter and lamp replacements.
Optional: Reverse Osmosis
Reverse osmosis (RO) removes dissolved minerals, fluoride, arsenic, and many chemicals. Install an under-sink RO unit ($300 to $900) for drinking and cooking water only — not whole-house use. RO wastes 3 to 5 gallons for every gallon it produces. Replace RO membranes every 1 to 2 years.
Gravity Filters
Berkey and similar gravity-fed ceramic filters ($200 to $400) need no electricity. They filter 2 to 4 gallons per hour and work well as a backup or for drinking water only. Filter life: 3,000 to 6,000 gallons.
Water Testing
Test new water sources before you drink. Basic bacteria and nitrate tests cost $50 to $100. Full panels including metals and chemicals cost $200 to $400. Test once a year after that. Your county health department or a certified lab can run the tests.
Costs, Legal Rules, and Common Mistakes
Rainwater System — About $2,000 to $8,000
Gutters, first-flush diverter, 500 to 1,000 gallon poly tank, basic plumbing, and three-stage filtration. Best for moderate to high rainfall areas with enough roof area. Lowest running cost after install.
Well System — About $5,000 to $18,000
Drilling, casing, submersible pump, pressure tank, and basic filtration. Best for dry climates or properties without enough roof area for rainwater. Steady supply year-round.
Spring System — About $2,000 to $6,000
Collection box, buried pipe, storage tank, and filtration. Only applies if you have a usable spring on site. Lowest running cost if gravity-fed.
Rainwater Laws
Rules vary by state. Most eastern and midwestern states allow residential rainwater collection. Some western states limit collection because of water rights laws — water that hits your roof may legally belong to downstream users in those states.
Texas, Ohio, and Virginia actively support rainwater use. Colorado, Utah, and Nevada have restrictions or registration requirements. Always check your state and county before installing tanks.
Well Permits
Nearly every state requires a permit to drill a well. Your county health department or water agency handles this. Expect a fee of $50 to $500. Wells must meet setback rules from septic systems (usually 50 to 100 feet). Water testing is required before use in most counties.
Common Mistakes
Sizing storage for average use instead of dry-season shortfalls. Skipping the first-flush diverter and getting poor water quality from roof debris. No backup plan when a pump fails or a drought empties the tank. Drinking untreated well or rainwater water without testing. Installing tanks before checking if rainwater collection is legal in your county. Using a pump that is too small for your well depth. Forgetting that UV filters only work on clear water — clogged sediment filters must be changed on schedule.
Frequently Asked Questions
Related Resources
Sources & References
Federal guidance on well water testing and safety
Rainwater harvesting standards and resources