__NOTOC__<small-title />[[Image:Plastic-lined_tank_icon.png|right|80px]][[Image:PlasticLinedTank.jpg|thumb|right|200px|]]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:
* A cylinder of sheet metal containing a large (eg. 1 ,500 liter) reinforced plastic bag . * a A plastic liner reinforced with a 10 ,000 liter plastic bag, installed in a hole in the ground.
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.
The Water extraction can be done with [http://ideorg[Handpumps]] or [[Small and efficient motor pumps]].org organisation IDEA [[Rope and bucket|bucket and rope] in Asia is developing several models ] can be used but risk of plastic-lined tankscontamination increases. In such a case, household water treatment should be advocated.
The organisation [http://wwwideorg.akvoorg 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.org/rsr/project/16/ 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%. {| border="1" cellpadding="5" cellspacing="0" align="center"|-! width="50%" style="background:#efefef;" | Advantages! style="background:#f0f8ff;" | Disadvantages|-| valign="top" | - Low cost rehabilitation alternative to metal or ferro-cement tanks.<br>- Take the shape of impluvia with PVC liner in Madagascar] 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 CRS and Practicasharp objects. <br>- May require replacement after some time (if exposed to ultra violet rays), has very nice photographs of hence need for shading/covering to protect the process of installing these type of tankslining.|}
==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.
{{procontable ===Construction, operations and maintenance===[[Image:PlasticLining.jpg|thumb|right|200px| pro=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 alternative to metal or ferro-cement 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.<br>| con= }}
==ConstructionDesign of the tank shape and size based on the soil type, operations which dictates the side slopes. For stable and unstable soils the side slopes are recommended to be 1:1 and maintenance==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>
* Polypropylene is an expensive material but it is the most durable pond liner material in existence because it can last for up to 40 years. Polypropylene, however, is not as flexible as EPDM liners.
* EPDM (Ethylene Propylene Diene Monomer) rubber liners are recommended for most pond installations because of their delicate balance between longevity, flexibility, affordability, and their lack of toxic plasticizers. Because EPDM liners are rubber-based, they are extremely flexible (much more so than PVC liners) - the extra flexibility of EPDM comes in handy when working with irregular folds and shelves that are commonly found in a pond. They also do not contain any plasticizers that can make the liner brittle and crack with age. A 45-mil EPDM liner can last for up to 20 years because of its natural resistance to UV, and its puncture resistance.
* Care needs to be taken with cheap linings – in some areas with swelling clay and differential settlement, linings can easily crack. The areas where cheap linings might work therefore may be site-specific, and depend on the clay content of the soil. For plastic linings, experience from India shows that these can be punctured by rodents, crabs or insects if there is no rodent/insect-proof layer before the plastic.
'''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==Field experiences==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.
==Reference manuals, videos, and links=Costs===* [httpPlastic 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/wwwmud frame with plastic lining the inside.ideorgWhile 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.org www6 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.ideorgIssues with this kind of tank in some places is that termites can eat the wood.org ] * [httpRound bamboo tanks are made in a similar way where bamboo gives external support to a plastic lining://wwwcosts are US$10 - US$15.5 (e.practicafoundationg.org www1.practicafoundation5m3 for US$23; 23m3 for US$233).org ]
===Manuals, videos and links===
* [http://worldagroforestry.org/projects/searnet/index.php?id=75 Plastic Lined Underground Tank: An Appropriate Water Reservoir for Small Scale Framers and Households]. Searnet.
* [http://www.ideorg.org/OurTechnologies/WaterStorageSystems.aspx IDE]. Low cost plastic storage bags.
* [http://www.lenntech.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.westernliner.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.