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Trickle Fill Water Systems
Overview
A "trickle fill" system is an efficient, environmentally friendly way of diverting water from a stream while maintaining a minimal impact on stream conditions. In a trickle fill system, water is diverted from a stream and gravity-fed through a pipe to an intermediate holding tank. Water in this holding tank can then be either pumped to a gravity flow storage tank for household use or directly fed to the household. The benefit of this system is that the stream is not overburdened by sudden withdrawls of large quantities of water, and yet immediate water demand can be conveniently met provided the two water tanks are large enough.
Design
Pipe Diameters
The pipe diameter should be minimized to what is needed to assure that total diversion doesn't exceed more than 1.5 days water demand. Pumping of water should not be done directly from streams except where there is insufficient drop (difference in elevation of the two tanks) on the property to allow for gravity flow into an off-stream water tank.
Intake Pipe Gradient (% Slope) |
Gallons Water Delivered Per Day Based on Stream Intake Pipe Diameter (inches) For Schedule 40 PVC Pipe |
Minimum Elevation Change (Feet) From Storage Tank To House for Different PSI (Based on 2" Schedule 40 PVC Pipe) |
TOTAL Minumum Elevation Change Needed For System Based on Desired PSI |
1/4" |
3/8" |
1/2" |
1.0" |
20 psi |
25 psi |
30 psi |
40 psi |
20 psi |
25 psi |
30 psi |
40 psi |
1% |
123 |
358 |
762 |
4,720 |
46 |
57.5 |
69 |
92 |
46 |
57.5 |
69 |
92 |
2% |
179 |
520 |
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Average Daily Water Consumption Per Household (Gallons) |
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3% |
223 |
648 |
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4% |
260 |
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1 |
2 |
3 |
4 |
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5% |
294 |
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300 |
600 |
900 |
1,200 |
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6% |
324 |
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Minimum Storage Tank Size For 7 Day Reserve (Gallons) |
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7% |
352 |
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8% |
379 |
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2,400 |
4,800 |
7,200 |
9,600 |
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9% |
402 |
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Minumum Storage Tank Size For Reserve and Fire Protection (Gallons) |
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10% |
427 |
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11% |
452 |
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4,900 |
9,800 |
14,700 |
19,600 |
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*- Assumes pipe full with water at ambient temperature and under turbulent flow with a roughness coefficient of 140. Orange shade area indicates pipe size and slope require flow valve and overflow return pipe |
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When direct pumping from a stream is required because of physical constraints to “trickle” gravity flow to water tanks, pump and tank systems should be designed with short duration pumping and low volume cycles typical of pressure bladder tank systems in order to minimize impacts on stream flows.
Fish Exclusion
Provide adequate fish screening of all surface water diversions to prevent the entrapment of fish and amphibians. In order to function properly, screens should be oriented parallel to flow and should have an opening size no larger than 3/32" in diameter. Take care to keep your screens in good repair and free of algae, leaves, or other debris.
Pump and Intermediate Tank Sizing
Size intermediate storage tank and pump to meet demand using the following criteria:
- The minimum intermediate storage tank size should be approximately 1.5 times the maximum water load to be pumped. For individual households, a 500 gallon tank for daily pumping would be adequate in most instances. Actual tank size will depend on frequency of pumping and water demand. If fire protection flow storage is proposed to be combined with storage tank capacity, increase the size of the tanks accordingly.
- Consider pump capacity and design options based on risk of freeze, maximum lift and volume, power supply, fire flow objectives, and other site specific factors. Pumps placed inside tanks or underground should be considered in areas subject to freeze.
Primary Water Storage Tank and Water Line Sizing
Tank(s) designed to store water for extended periods should be of sufficient size to meet water reserve and fire reserve capacities. The water line from the primary water storage tank(s) should be sized to meet fire flow requirements where applicable.
Inlet Flow Control and Return Flow
When pipe diameter and pipe slope gradient result in flows that exceed intermediate tank storage capacity install a valve (e.g. quarter turn or straight valves) to control flow rates and install a stream return/overflow pipe to return excess flows back to the stream.
Backflow Prevention
Where water is pumped up to a higher tank, pond or reservoir, install a one way backflow prevention valve near the primary storage tank(s), pond or reservoir to minimize water losses in the event of a pipeline break.
Primary Tank Supplemental Fill Capability
Consider installing a water connection to allow water trucks or other water deliveries to refill primary tanks if needed, such as when stream flow is insufficient to meet water needs.
Resources for Additional Ideas & Information
Funding for this project comes from: California Environmental Protection Agency State Water Resources Control Board
Funding for this project has been provided in full or in part through an agreement with the State Water Resource Control Board. The contents of this document do not necessarily reflect the views and policies of the State Water Resources Control Board, nor does mention of the trade names or commercial products constitute endorsement or recommendation for use.
(Gov. Code. 7550; 40 CFR 31.20)
Funding support to create more user-friendly, detailed information in order to facilitate better water resources management and public awareness also was generously provided by the State of California Department of Water Resources (DWR), from the Safe Drinking Water, Water Quality and Supply, Flood Control, River and Coastal Protection Bond Act of 2006 via Humboldt County on behalf of the seven county North Coast Resource Partnership region under the North Cost Integrated Regional Water Management Plan (NCIRWMP) Proposition 84 Planning Grant.
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