Hawaiʻi Home Wise

Calculator assumptions and page copy reviewed July 13, 2026. Replace defaults with current bills, rate sheets, and written quotes.

Free planning tools · made in Hawaiʻi

Hawaiʻi Water Catchment Sizing + Cost Calculator

Estimate household water storage needs, roof collection potential, dry-day buffer, and basic pump electricity cost for Hawaiʻi catchment homes.

Made for Hawaiʻi buyers, owner-builders, off-grid families, and homeowners comparing tank/filter/pump upgrades

Local inputsHawaiʻi rates and cost categories

Visible mathEvery formula is shown

Your numbersNo account or data upload

Built for decisionsCopy results into quote requests

Choose the decision in front of you

Sixteen practical calculators. No login.

Start with the rough number, then use the local notes and quote questions to find what the estimate leaves out.

Live calculator

Catchment Sizing

Estimate Hawaiʻi catchment tank size, dry-day storage gap, monthly collection, and pump electricity—then open maintenance, testing, and buyer checklists.

Take the math with you

Copyable result summary

Paste the same assumptions into texts, emails, and quote requests.

Local notes

Catchment is water math plus maintenance discipline

For Hawaiʻi buyers, catchment is not just “does it have a tank?” It is roof area, dry days, family use, filters, pump power, water testing, and what happens when something fails.

  • Dry-side and wet-side assumptions change the answer fast.
  • Pump electricity is small compared with tank decisions, but it reminds readers this is a system.
  • Best next step: confirm tank size, roof collection, filters, UV, pump condition, and water testing history.

Before you spend

Questions the estimate cannot answer

  • How many dry days would make me nervous?
  • Is the existing tank enough for the actual household?
  • What filter/UV/testing maintenance is required?
  • What catchment inspection item would make me pause before buying?

Comparable facts

Catchment planning line comparison

Tank size is only one line in the water path. Storage, treatment, testing, pump power, and delivered-water reserves belong in the same plan.

Household demandDaily use = people × gallons/person/day. For Hawaiʻi buyers, catchment is not just “does it have a tank?”
Dry-day bufferMany households start with 14–30 days as a planning range, then adjust for rainfall zone, delivery access, and risk tolerance. How many dry days would make me nervous?
Tank size vs recommended storageRecommended storage = daily use × dry-day buffer. Is the existing tank enough for the actual household?
Roof collection areaRain collection = roof sq ft × rain inches × 0.623 × 80% collection factor. Dry-side and wet-side assumptions change the answer fast.
Pump electricityCatchment is not only tank size. Pumps, pressure systems, filters, UV, and maintenance all affect true ownership cost.

Transparent math

How this estimate works

  • Daily use = people × gallons/person/day
  • Recommended storage = daily use × dry-day buffer
  • Rain collection = roof sq ft × rain inches × 0.623 × 80% collection factor
  • Pump kWh = watts ÷ 1000 × runtime hours

Planning estimate only. Verify rates, equipment specs, tax details, permitting, utility rules, and safety requirements before spending money.

Next step

Buying or fixing a catchment home?

Size is only the start. Continue with maintenance cost, water testing, and the buyer inspection path.

Open catchment water planning

Save your packet

Hawaiʻi catchment buyer inspection packet

Run the calculator, then download a text packet with your summary and the questions to send contractors or movers. Nothing uploads automatically.

  • Recommended storage, tank gap, and monthly collection from the calculator
  • Roof, gutter, tank, pump, filter, UV, and pressure-system condition notes
  • Maintenance and water-testing dates to request from the seller
  • Pump electricity assumption and island utility rate used

Open the catchment buyer checklist

Reality check

Do not let a clean estimate look more certain than it is

  • Use recent Hawaiʻi rates and written quotes, not mainland averages.
  • Ask what is excluded: permits, trenching, rock, repairs, financing, insurance, or maintenance.
  • If the answer changes a major purchase, verify it with the right local professional.

After the sizing estimate: inspect the whole roof-to-tap path, budget upkeep, and write the testing plan.

InspectBuyer checklist BudgetMaintenance cost PlanTesting schedule RecordsProperty research HubCatchment center

After the estimate

Use the result with official sources and checklists

Copy the summary into quote requests, then open the matching resource path. The professional directory remains an early research aid, not a paid ranking.

Open homeowner resources Research a property Send a correction

Important limits

Safety + estimate disclaimer

These tools are educational planning estimates only. Actual savings and costs depend on local conditions, rates, equipment, financing, written quotes, eligibility, permits, and approvals.

Electrical safety: hardwired EV chargers, service panels, transfer switches, solar inverters, and battery systems should be evaluated and installed by licensed professionals. Do not perform electrical work unless qualified and legally permitted.

Common questions

FAQ

How big should a Hawaiʻi catchment tank be?

A common starting point is enough storage for household use times a dry-day buffer—often two to four weeks on wetter coasts and longer on dry leeward areas. Replace rainfall and use defaults with local records.

Is catchment water safe to drink?

Safety depends on roof, tank, filtration, UV/chlorination, maintenance, testing, and local guidance. This calculator only estimates sizing and energy.

What dry-day buffer should I use?

Many households start with 14–30 days as a planning range, then adjust for rainfall zone, delivery access, and risk tolerance.

Does rainfall vary by island?

Yes. Hilo-side Hawaiʻi Island, windward Oʻahu/Maui, and dry Kona or leeward areas need different assumptions.

Why include pump electricity?

Catchment is not only tank size. Pumps, pressure systems, filters, UV, and maintenance all affect true ownership cost.