__NOTOC__<small-title />[[Image:Plastic-lined_tank_icon.png|right|80px]][[Image:PlasticLinedTank.jpg|thumb|right|400px200px|]]Plastic-lined tanks can be either above ground, partially buried, or entirely below ground.
A low cost alternative to metal or ferrocement tanks for storing of water are plastic-lined tanks. Several models have been developed, for example:
Open storage tanks can be made of earth. If clay is not available, a plastic lining is needed to stop water from leaking away. Linings can be made of standard plastic sheet glued together with the tar normally used to repair roofs. The plastic must be covered with earth to prevent it from being exposed to the sun.
Water extraction can be done with [[Handpumps]] or [[Small and efficient motor pumps]]. A [[Rope and bucket|bucket and rope]] can be used but risk of contamination increases. In such a case, household water treatment should be advocated.
The organisation [http://ideorg.org IDE] in Asia is developing several models of plastic-lined tanks.
===Suitable conditions ===
* Rainwater harvesting requires at least an annual rainfall of 100-200 mm. Depending on the size of the design; the tank has a capacity of 1,500 to 10,000 liter.
* Shading can reduce evaporation by around 30%.
{{procontable | pro=
- Low cost alternative to metal or ferro-cement tanks.<br>
| con=
- If the tank is not fenced, animals walking on the roof can damage it.
}}
{| border="1" cellpadding=Construction, operations and maintenance"5" cellspacing="0" align="center"|-! width="50%" style="background:#efefef;" | Advantages! style="background:#f0f8ff;" | Disadvantages|-| valign="top" | - Low cost alternative to metal or ferro-cement tanks.<br>- Take the shape of the dug pit/reservoir. <br>- Easy to secure to the side wall. <br>| valign="top" | - If the tank is not fenced, animals walking on the roof can damage it.- May be torn or pricked by sharp objects. <br>- May require replacement after some time (if exposed to ultra violet rays), hence need for shading/covering to protect the lining.|}
===Construction, operations and maintenance===
[[Image:PlasticLining.jpg|thumb|right|200px|Catholic Relief Service (CRS) is implementing a project to rehabilitate impluvia (underground water catchment basin) with local PVC liner. It will also put in place a management committee, which will be trained after rehabilitation as well.]]
[http://www.akvo.org/rsr/project/16/ Low cost rehabilitation of impluvia with PVC liner in Madagascar] by CRS and Practica, has very nice photographs of the process of installing these type of tanks.
Design of the tank shape and size based on the soil type, which dictates the side slopes. For stable and unstable soils the side slopes are recommended to be 1:1 and 1:2 respectively.
====Choosing a lining====
Below the pros and cons of various liners are discussed. There are five main types of liner constructions: Polyethylene, Polythylene, PVC liners, EPDM/rubber, and polypropylene. As an indication of costs, an EPDM/rubber sourced in the UK is around $6.5 per square metre not including shipping costs.
'''Plastic/rubber''': <br>
A plastic/rubber lining is not an option in most circumstances due to combinations of fragility, expense and feasibility for welding together sheets for larger ponds. Below the pros and cons of various liners are discussed. There are five main types of liner constructions: Polyethylene, Polythylene, PVC liners, EPDM/rubber, and polypropylene. As an indication of costs, an EPDM/rubber sourced in the UK is around $6.5 per square metre not including shipping costs.
'''Choice of lining needs further consideration''':<br>
'''Sheet size''': <br>
* Ideally we should not have to weld sheets together in situat the tank site.
* The main advantage of polypropylene is that it comes in large sheets larger than 50’ x 100’. If you are building an extremely large pond, polypropylene may be a viable option.
* A limitation of EPDM is its size they typically arrive in sheets ranging from 5’ x 10’ to a 50’ x 100’ roll.
====Materials====
* Remember to include lining material for anchoring when ordering.
Material needed for a tank of 5 m3:
* 12 m2 of plastic sheet
* 3 m of PVC tube
==Costs==Maintenance====Support the capacity of the government or private sector to be able to provide (for payment) a tankering scheme to fill tanks during the driest parts of the year.
==Field experiences=Costs===Plastic lined tanks made from weaker/cheaper wall materials have proved to be cheap: US$6.7 - US$10 per m3 of storage (e.g. 6m3 for US$40 for the sheeting & iron sheets, while labour/mud provided by householder). These tanks are made using a wood/mud frame with plastic lining the inside. While the feedback from trials in Uganda indicate that the plastic does not last more than 2 years (due to being punctured by something), because the plastic sheet is cheap ($1.6 per m3 of storage), it seems that this recurring cost is a lot more affordable than much larger one-off costs for more robust tanks. Issues with this kind of tank in some places is that termites can eat the wood. Round bamboo tanks are made in a similar way where bamboo gives external support to a plastic lining: costs are US$10 - US$15.5 (e.g. 1.5m3 for US$23; 23m3 for US$233).
==Reference manuals=Manuals, videos, and links===* [http://wwwworldagroforestry.org/projects/searnet/index.php?id=75 Plastic Lined Underground Tank: An Appropriate Water Reservoir for Small Scale Framers and Households].ideorgSearnet.org * [http://www.ideorg.org /OurTechnologies/WaterStorageSystems.aspx IDE] . Low cost plastic storage bags.* [http://www.practicafoundationlenntech.org com/small-community-water-supplies.htm#ixzz2TsbJyNk6 Water supply in small communities], by Lara Fabrizi. Includes how best to manage the planning, construction, and operation and maintenance of water projects or tanks.* [http://www.practicafoundationwesternliner.org com/ Liner material]. Western Environmental Liner.
===Acknowledgements===* CARE Nederland, Desk Study: [[Resilient WASH systems in drought-prone areas]]. October 2010.* [http://worldagroforestry.org/projects/searnet/index.php?id=75 Plastic Lined Underground Tank: An Appropriate Water Reservoir for Small Scale Framers and Households]. Searnet.