Why Rainwater Harvesting Makes Financial and Environmental Sense
The average American home uses 80–100 gallons per person per day, with 30% used outdoors for irrigation. Municipal water treatment and distribution consumes roughly 0.005 kWh per gallon — meaning a home that collects 30,000 gallons annually saves about 150 kWh of energy and avoids 138 lbs of CO₂ emissions, in addition to reducing your water bill. In high-cost water regions like California, Arizona, and the Northeast, systems can pay back in as little as 3–5 years.
Understanding Monthly Surplus and Deficit Months
Annual collection totals can be misleading. In Seattle, 90% of rainfall comes between October and April — meaning summer irrigation demand must be met by stored water from wet-season surplus. In Houston and Miami, summer thunderstorms peak precisely when outdoor demand is highest. Using the Supply vs Demand tab to model month-by-month dynamics reveals which months you'll rely on tank storage and whether your tank is properly sized to bridge dry periods.
Right-Sizing Your Tank
Tank sizing depends on how long your longest deficit run is. If you have 3 consecutive deficit months where demand exceeds collection, your tank needs to store at least 3 months of your monthly need. A general rule: size your tank for 30–60 days of demand in drought-prone areas. Too-small tanks fill and overflow, wasting water; too-large tanks may never fill in low-rainfall climates. The overflow figure in the Supply vs Demand tab tells you exactly how much water you're wasting with your current tank.
Legality, Permits, and HOA Rules
As shown in the System Planner tab, rainwater collection is legal in 47+ states, with only Colorado and Utah having significant volume restrictions. However, local ordinances and HOA rules may be more restrictive than state law. Texas actively encourages collection with a sales tax exemption on equipment. Arizona and New Mexico offer tax incentives. Always verify local rules before installation, especially for underground cisterns that may require permits.
Water Quality and Treatment Options
Collected rainwater is naturally soft and slightly acidic (pH 5.5–6.5), ideal for most plants. For toilet flushing and laundry, a simple mesh screen plus first-flush diverter is sufficient. For potable use, a full treatment train is required: sediment filter → activated carbon → UV sterilization → optional reverse osmosis. Green roofs and asphalt shingles can leach organic compounds; metal and EPDM roofs produce the cleanest water. Regular tank cleaning (annually) and filter replacement are the primary maintenance requirements.