Water is something most of us don’t think about until the taps run dry. Whether you are at home or running a business, a water outage causes real problems. From daily inconvenience to lost revenue, it’s easy to see why more people are installing backup water systems with pumps to keep things running.
Why Backup Water Matters
In South Africa, supply is not always guaranteed. Burst pipes, municipal repairs or drought restrictions can leave you without water for hours or days. A backup system stores clean water and makes it available on demand. For homes, that means less stress. For businesses, that means avoiding downtime.
The Role of Pump Installations
A storage tank on its own is not enough. You need a pump to deliver steady pressure to taps, showers and equipment. A correctly sized pump makes the changeover from municipal to backup automatic and smooth. In most setups you will not even notice when the system takes over.
The Benefits You Will See
Uninterrupted supply
Stay prepared for outages and shortages.
Comfort and convenience
Keep bathrooms, kitchens and equipment working.
Better water pressure
A pump keeps flow and pressure consistent across your property.
Tailored solutions
Homes, complexes and commercial sites can be designed to fit need and budget.
Cost control
Avoid losses from shutdowns, emergency water purchases and wasted staff time.
How to Calculate the Right Tank and Pump Size
You can size a system in five quick steps. Use the formulas and examples below. If you prefer, we can do this for you after a short site call.
Step 1: Estimate daily water use
Pick the method that fits your site.
- Household rule of thumb
Daily use ≈ number of people × 150 to 200 litres per person
Example: 4 people × 180 L = 720 L/day - Fixture method
Add typical daily volumes for toilets, showers, washing, kitchen and irrigation.
Example:
Toilets 4 flushes/person × 6 L × 4 people = 96 L
Showers 8 min × 8 L/min × 4 people = 256 L
Kitchen and laundry ≈ 250 L
Irrigation ≈ 150 L
Total ≈ 752 L/day (close to the rule of thumb) - Business or commercial
Use process data or guidelines per headcount and activity.
Office: 25 to 40 L per person per day
Restaurant: 70 to 120 L per cover per day
Guesthouse: 150 to 250 L per occupied room per day
Light manufacturing: measure processes and cleaning cycles
Step 2: Decide how many outage days to cover
Coverage days = the longest realistic time you want to ride through.
Common choices: 1 to 3 days for homes, 2 to 5 days for businesses.
Step 3: Calculate tank size with a safety buffer
Tank size (L) = daily use × coverage days × safety factor
Safety factor accounts for hot days, leaks and growth. Use 1.2 to 1.5.
Home example
Daily use = 720 L
Coverage = 2 days
Safety factor = 1.3
Tank = 720 × 2 × 1.3 = 1 872 L → choose 2 000 L tank
Restaurant example
100 covers/day × 90 L = 9 000 L/day
Coverage = 2 days
Safety factor = 1.2
Tank = 9 000 × 2 × 1.2 = 21 600 L → choose 20 000 to 25 000 L split over multiple tanks
Step 4: Size the pump for pressure and flow
Two simple checks get you 90 percent of the way there.
A. Required pressure at the outlet
Target pressure at taps: 2.5 to 3.5 bar for homes
Add static head: 0.1 bar per metre of height from pump to highest outlet
Add friction allowance: 0.5 to 1.0 bar for pipe losses
Required pump pressure = outlet target + static head + friction
Example home
Outlet target = 3.0 bar
Highest shower is 5 m above pump → 0.5 bar
Friction allowance = 0.5 bar
Required = 3.0 + 0.5 + 0.5 = 4.0 bar
B. Required flow rate
Pick the worst case of simultaneous use.
Typical flow rates
Shower 8 to 10 L/min
Basin 4 to 6 L/min
Kitchen sink 6 to 8 L/min
Toilet fill 4 to 6 L/min
Irrigation zone 15 to 25 L/min
Example home worst case
Two showers + kitchen sink = 10 + 10 + 8 = 28 L/min
Choose a pump that can deliver 28 L/min at 4.0 bar
Tip for businesses
List peak simultaneous fixtures or process loads. Add 10 to 20 percent margin.
Step 5: Choose layout and controls
Direct pressure system
Pump feeds house directly. Simple and fast response.
Pressure vessel with VSD
Pump with a small pressure tank and a variable speed drive. Smooth pressure, quiet running, efficient.
Header tank
Pump fills a small elevated tank, then gravity feeds. Good stability, slower response.
Automation
Level switches in the tank
Auto changeover valve to municipal supply
Dry run protection on the pump
Backflow prevention to protect municipal lines
Sediment filter before the pump to protect it
Water Quality and Maintenance
- Protect the pump
Fit a washable sediment filter before the pump. Clean monthly. - Keep stored water fresh
If the tank only serves outages, aim to turn it over at least once a month.
Turnover check: average monthly use should be similar to tank volume.
If turnover is low, use a smaller tank or plan a monthly drawdown and refill. - Disinfection
Closed tanks stay cleaner. If you also collect rainwater or borehole water, include a cartridge filter and optional UV or chlorine dosing based on use. - Annual service
Check pump pressures, valves, strainers, electrical connections and tank integrity.
Quick Reference Table
| Site type | Daily use guide | Coverage days | Tank size guide | Pump guide |
|---|---|---|---|---|
| 3 to 4 person home | 500 to 800 L | 1 to 2 | 1 000 to 2 000 L | 25 to 35 L/min at 3.5 to 4.0 bar |
| Large home or small B&B | 1 000 to 2 500 L | 2 to 3 | 3 000 to 7 500 L | 40 to 60 L/min at 4.0 to 4.5 bar |
| Office 20 people | 600 to 800 L | 2 | 1 500 to 2 000 L | 20 to 30 L/min at 3.5 to 4.0 bar |
| Restaurant 100 covers | 7 000 to 12 000 L | 2 | 15 000 to 25 000 L | 60 to 120 L/min at 4.0 to 5.0 bar |
An Investment in Reliability
A backup water and pump system protects your comfort at home and your productivity at work. It gives you control when the municipal supply is out and keeps your property usable.
At Green Power Solutions, we survey your site, calculate the right tank, select the correct pump and install the controls that make it all automatic. If you would like a quick proposal, tell us how many people use the site, how many outage days you want to cover and the number of simultaneous fixtures you expect. We will do the rest.