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A pump that only needs to lift water 20 feet vertically must overcome about 8.7 psi of static pressure. But you should not choose a pump based on the 20-foot lift alone.
You also need enough pump capacity for:
- The flow rate you want
- Friction loss in the pipe or hose
- Any filter, valve, or fitting losses
- The pressure you want where the water comes out
For most rainwater systems, the best way to size the pump is by total dynamic head, or TDH, rather than horsepower.
What Does a 20-Foot Lift Mean?
Vertical lift creates pressure that the pump must overcome.
A useful conversion is:
2.31 feet of water = about 1 psi
For a 20-foot rise:
20 ÷ 2.31 = about 8.7 psi
So a pump needs at least 20 feet of head just to move water to that height.
That does not mean a pump rated for exactly 20 feet of head is a good choice. At its maximum head rating, many pumps produce little or no usable flow.
You need some extra capacity.
Calculate the Total Head the Pump Needs
Start with:
Total dynamic head = vertical lift + pressure requirement + friction losses
All parts should be converted to feet of head.
For example, suppose you want to move rainwater:
- 20 feet uphill
- Through 75 feet of hose
- At about 10 gallons per minute
- With 20 psi available at the outlet
The 20 psi outlet pressure equals:
20 × 2.31 = 46.2 feet of head
Before accounting for hose friction, your pump already needs:
20 + 46.2 = 66.2 feet of head
Pipe, fittings, valves, and filters add more resistance. The pump might therefore need to deliver your target flow at something around 70 feet of total head or more.
The exact number depends on the plumbing.
How Much Head Do You Need for Different Uses?
The required pump size changes greatly depending on what happens after the 20-foot lift.
| Use | Main requirement |
|---|---|
| Moving water from one tank to another | Mostly vertical lift and pipe friction |
| Filling a garden tank uphill | Lift plus moderate flow |
| Running an open garden hose | Lift plus some outlet pressure |
| Drip irrigation | Lift plus the pressure required by the drip system |
| Sprinklers | Lift plus considerably more operating pressure |
| Supplying a house | Lift plus household pressure and peak flow |
If you are simply transferring water to another open tank 20 feet higher, the required pump may be fairly small.
If you want strong pressure at a faucet or sprinkler after lifting the water 20 feet, you need much more head.
Do Not Size the Pump by Horsepower Alone
A 1/2-horsepower pump is not automatically suitable, and a 1-horsepower pump is not automatically better.
Two pumps with the same horsepower can have very different combinations of:
- Flow rate
- Maximum head
- Pressure
- Pump design
Instead, check the pump's performance curve.
The curve shows how many gallons per minute the pump can deliver at different amounts of head.
For example, you might need:
8 GPM at 60 feet of total head
Look for a pump whose performance curve shows that it can actually supply about 8 GPM at 60 feet.
Do not use the pump's maximum-flow number. That number is usually measured with very little resistance.
Do not use its maximum-head number either. At maximum head, flow normally falls close to zero.
How Much Flow Do You Need?
Flow rate is normally measured in gallons per minute, or GPM.
A simple water-transfer system may only need a few GPM. Irrigation or household use can require much more.
Think about what will run at the same time.
For example, moving rainwater slowly from an IBC tote to an uphill storage tank does not require the same pump as running several sprinklers.
Higher flow also causes more friction loss inside the pipe.
That means increasing the required GPM can increase the required pump head even when the vertical lift stays at 20 feet.
Pipe Size Matters
Small pipes and long hoses create resistance.
This resistance is called friction loss.
A long, narrow garden hose can use a significant part of a pump's available pressure. Larger pipe usually reduces that loss.
Friction increases when:
- The pipe gets longer
- The pipe diameter gets smaller
- Flow rate increases
- More elbows and fittings are added
- Filters become clogged
For a long 20-foot lift, increasing the pipe diameter can sometimes improve performance more effectively than simply installing a larger pump.
Is the Pump Below or Above the Water?
This is an important difference.
Pump Below the Water or Submerged
If the pump is submerged in the tank, or water naturally flows into its inlet, the pump mainly has to push water upward.
A 20-foot discharge lift is usually straightforward if the pump has enough head capacity.
Submersible pumps are commonly used in cisterns and other rainwater tanks for this reason.
Pump 20 Feet Above the Water
This is a different problem.
A surface pump trying to pull water upward has a suction lift.
The theoretical limit for suction at sea level is roughly 34 feet, but real pumps cannot reliably operate at that theoretical limit. Elevation, water temperature, pipe friction, air leaks, and pump design reduce practical suction ability.
A claimed maximum suction lift should not be treated as a normal operating point.
Use transfer-pump distance limits to compare likely priming faults behind unstable delivery pressure.
If the water level can be about 20 feet below a surface pump, check the manufacturer's allowed suction lift carefully. Keeping the pump closer to the water or using a submersible pump is often a more dependable arrangement.
How Much Pressure Does a 20-Foot Lift Use?
Every 2.31 feet of elevation uses about 1 psi.
So:
- 10 feet uses about 4.3 psi
- 20 feet uses about 8.7 psi
- 30 feet uses about 13 psi
- 50 feet uses about 21.6 psi
- 100 feet uses about 43.3 psi
Suppose a pump produces 40 psi at a certain flow.
If the water must rise 20 feet, about 8.7 psi is needed just for elevation.
That leaves roughly 31 psi before subtracting friction and other losses.
Example: Pumping Rainwater 20 Feet Uphill
Suppose you have an IBC tote at the bottom of a slope and want to send water to another tank 20 feet higher.
The upper tank is open to the atmosphere, so you do not need extra pressure inside it.
Your basic requirement might be:
20 feet vertical head + plumbing friction
If the plumbing adds another 5 to 10 feet of head at your target flow, you might need the pump to provide the desired GPM at roughly 25 to 30 feet of head.
A pump with a maximum head of only 30 feet would be a poor choice because its flow could be very low near that point.
Instead, look for a pump whose curve shows comfortable flow at your actual operating head.
Example: Pumping 20 Feet to a Garden Hose
Suppose the hose outlet is 20 feet higher and you want about 30 psi at the hose.
Convert the desired pressure:
30 × 2.31 = 69.3 feet
Add the elevation:
69.3 + 20 = 89.3 feet
Then add hose and fitting losses.
Your real requirement might therefore exceed 90 feet of total dynamic head.
This is why a pump that easily transfers water 20 feet uphill may still give weak pressure through a garden hose.
Example: Pumping 20 Feet to a House
Household supply normally requires both pressure and adequate flow.
Suppose you want approximately 40 psi available at the house:
40 × 2.31 = 92.4 feet of head
Add the 20-foot elevation:
92.4 + 20 = 112.4 feet
Then add plumbing, treatment, and filter losses.
The pump would therefore need to provide your required household flow at more than 112 feet of total head.
A pressure tank, pressure switch, controls, dry-run protection, plumbing design, and electrical requirements may also be involved.
A pump used for household water should be designed as a pressure system rather than chosen as a simple transfer pump.
If rainwater will enter household plumbing, also follow local requirements for rainwater use, backflow protection, and separation from potable plumbing.
Leave Some Pump Capacity in Reserve
Avoid selecting a pump that operates right at its maximum head.
Actual system resistance can increase because of:
- Dirty filters
- Longer pipe runs
- Extra fittings
- Changes in water level
- Added equipment
- Higher-than-planned flow
Choose a pump that reaches your required flow comfortably at your calculated head.
A pump curve is more useful for this than a large maximum-head number printed on the box.
A Simple Pump-Sizing Method
Use these steps:
- Measure the vertical distance from the lowest water level to the highest discharge point.
- Decide how many gallons per minute you need.
- Decide how much pressure is needed at the outlet.
- Convert outlet pressure to head by multiplying psi by 2.31.
- Estimate friction losses through the pipe, hose, fittings, valves, and filters.
- Add these values to find total dynamic head.
- Check the pump curve for your required GPM at that head.
For a simple open-tank transfer:
TDH ≈ vertical lift + friction loss
For a pressurized outlet:
TDH ≈ vertical lift + desired pressure × 2.31 + friction loss
Frequently Asked Questions
Can a small pump lift water 20 feet?
Yes, if its pump curve shows adequate flow at more than 20 feet of head. A pump with a 20-foot maximum head is generally not enough because its flow will be very low near its maximum.
How much pressure does it take to lift water 20 feet?
A 20-foot vertical rise requires about 8.7 psi just to overcome gravity.
Is a 1/2 HP pump enough for a 20-foot lift?
It may be, but horsepower alone cannot answer the question. Check how much flow the specific pump delivers at your total dynamic head.
What maximum head should I look for?
Your pump's maximum head should be higher than your calculated operating head. More importantly, its performance curve should show the required GPM at the head your system will actually have.
Does horizontal distance count as head?
Horizontal pipe does not create elevation head, but it creates friction loss. A long hose can therefore require additional pump head even when it stays level.
Can a surface pump suck water up 20 feet?
Some surface pumps may operate with that suction lift, but 20 feet is demanding for many setups. Air leaks, elevation, pipe resistance, and pump design can cause problems. Check the manufacturer's suction-lift limit and consider placing the pump closer to the water or using a submersible pump.
Do I need more pump pressure for sprinklers?
Usually yes. The pump must overcome the 20-foot elevation and still provide the pressure and flow required by the sprinklers. Pipe friction must also be included.
