Rainwater collection is often a good option in areas with regular rainfall and where traditional water sources (i.e. groundwater, surface water) are not available or contaminated. The following ‘ho...(read full answer)
Rainwater collection is often a good option in areas with regular rainfall and where traditional water sources (i.e. groundwater, surface water) are not available or contaminated. The following ‘how to’ guide comes from my experience implementing Rain Water Harvesting Systems (RWHS) in the Solomon Islands, where many coastal communities don’t have others options for water supply.
The components of Rain Water Harvesting Systems (RWHS)
All RWHS are made of a four elements: a catchment area, a collection system, a storage reservoir and a water collection point.
Your catchment area would normally be a roof. Impermeable ground-level surfaces can also be used to catch rainwater. However, water caught on ground-level surfaces is usually of lower quality than raised surfaces, due to factors including dirty soil, wild defecation, agricultural chemicals and solid and liquid waste. So I’ll focus this guide on raised surfaces, such as roofs.
As you can guess, the bigger your roof, the better your catchment. You want to ensure you have the maximum runoff, by reducing the evaporation and infiltration through the roofing material. The runoff coefficient of a corrugated iron sheet is around 0.8 while for thatch it is 0.2. In Solomon Island, we used public buildings (i.e. schools and churches) for rainwater catchment and few private houses when we didn’t have any other option, making sure that it will be a shared RWHS. We even rehabilitated some of the roofs, using locally available corrugated sheets.
The collection system is made of gutters, placed on one or two sides of the roof, depending on its design. Always keep in mind that you want to get a maximum supply. In Solomon Islands, for gutters we used PVC spouting 150mm width and for downpipes PVC Ø100mm; which are the most common, the easiest to use and allowing a good water collection (limited losses of water and reduced frictions). Then, before the inlet of your reservoir, you need to install a 1st flush pipe – which is simply a vertical closed PVC pipe. The 1st rain will clean your roof and fill this flush pipe with dirty water rather than your reservoir. Quite useful.
The storage reservoir. It could be constructed – using local knowledge and skills, or bought fully equipped, installed outside, inside or even put underground. The local conditions, habits and expectations would guide you. Involve the concerned people during the assessment and design phases. But the reservoir capacity needs to be properly estimated, in order to store enough water for the dry season.
You can place the water collection point wherever you want, directly on the reservoir or further down, or even inside the house. The storage reservoir could also be put underground, with a pump would be needed to lift the water to where it is needed.
Design of the RWHS
Firstly, check if there is enough water to satisfy the demand, comparing the maximum water supply and the maximum demand of water. Then, calculate the required volume of the water storage, to make sure that there will be enough water in the dry season.
Maximum water supply:
Volume of water available [L] = Plan area of roof [m2] x Runoff coefficient [ratio] x Annual rainfall depth [mm]
Maximum water demand:
Volume of water needed [L] = Daily water need [L/day/person] x Nb of person to supply x Nb of days of supply desired
If Maximum water supply > Maximum water demand, the RWHS is feasible. If not, you need to change some of the parameters (i.e. roofing material, roofing surface, number of people served, number of days of supply) or to find another source of water.
Calculation of the volume of storage needed for the dry season:
A first estimation would give you an idea of the required size (and the required budget):
Minimum storage volume required [L] = Daily water demand [L] x Nb of days in the longest dry season
Then, you have to do detailed calculations, using monthly rainfall data. For this purpose, draw a table with 7 columns:
- Column A = Number of days in month
- Column B = Monthly demand [L] = Daily demand x A
- Column C = Monthly rainfall [mm]
- Column D = Monthly supply = Rainfall captured [L] = Catchment area [m2] x Runoff coefficient x C
- Column E = Stored in this month [L] = D - B
- Column F = Cumulative amount in storage [L] starting at the end of the dry season For example if the last month of the dry season is August, you'll start to fill the reservoir - and you'll start your calculation in September.
Then, the minimum storage of your reservoir should be the highest cumulative amount in storage, plus an additional volume allowing some mistakes, but also the volume of the first flush, the volume of water below the outlet and the air gap above the overflow.
Maintaining rainwater quality Rainwater is normally considered to be high quality with very low turbidity and zero faecal contamination. However, it can become contaminated after touching any surface, such as:
- The catchment area (i.e. dirty roofing);
- The collection system (i.e. dirty gutter);
- Or inside the storage tank.
So, keep in mind that a regular maintenance of the whole RWHS is crucial to keep water quality safe. The users need to be trained on it. Also, in some highly developed and industrialised urban areas, rainwater might contaminated by atmospheric pollutions. You should plan to check the rainwater quality by bringing samples to a governmental or private lab.
This is it. If you have any questions, do not hesitate to ask.
To see if you could have access to groundwater as a water supply in your area you need to conduct ‘groundwater prospecting’.
In brief, groundwater can be more or less easily exploited and can be f...(read full answer)
To see if you could have access to groundwater as a water supply in your area you need to conduct ‘groundwater prospecting’.
In brief, groundwater can be more or less easily exploited and can be found in: major aquifers, fracture zones, weathered zones, alluvial deposits and scree and/or river valleys.
During your groundwater prospecting, you are looking for signs and clues of structural characteristics for groundwater aquifers and you are trying to answer some basic questions such as: What are the main geological formations in this surveyed area? What kind of aquifer systems are presents? Where is the surface water infiltrating? Where is it not? Are there any traces of fractures? …
A preliminary study would allow you to accept or reject the groundwater as supply for the targeted population and if accepted, you’ll identify the most suitable technical solution. Then, the construction study would confirm you or not the utility of the selected aquifer and allow you to implement precisely the siting of the borehole or well. Finally, the construction itself, where you will assess in deep the resource and the borehole or well drilled or dug, equipped and tested.
Desk study: you need to collect and analyse the existing information (from national institutions, universities, geological centres, NGOs….) on the type of geological formations and aquifer systems, the climatic data (rainfall and temperature), the groundwater resources and technical solutions already tested and implemented locally (boreholes or wells; construction techniques, depth, diameters and yields of existing installations) and the costs and available resources (equipment, skilled personal, access, logistics). This first step is crucial and the assistance of local professionals will help you to understand the local area and its groundwater. Don’t stand alone!
Cartography: combined to the desk study and with the help of local professionals, topographic and geologic maps of the surveyed area would allow you to confirm/identify the structural features such as the geological formations, the vegetation cover, the relief, the hydrographic network (i.e. draining and infiltration zones), and so, the groundwater feeding and releasing zones.
Aerial/satellite images: assisted by professionals, you can appreciate on these images the vegetation covers (i.e. dry and humid zones), the structural features (i.e. fracture zones) and geomorphological (i.e. draining and infiltrating zones) features.
Field visit Following the preliminary study, the field visit would confirm and refine the collected and analysed data. It’s time to leave your office and discuss with people!
Preliminary visit: discussions with population and local authorities regarding the structural features (i.e. vegetation covers, relief, draining and flooded areas, geology), the water resources and their behaviour (i.e. wells, boreholes, springs, rivers and ponds; as well as abandoned and dry wells and boreholes; dry and wet seasons; water quality; history of these water resources). Then, you need to visit some sites, some specificities identified during the preliminary study and the discussions (i.e. depth and diameter of wells and boreholes, water quality, fractures, flooded areas); a GPS would be useful to transfer these information on maps.
Technical meetings: you need to get local and updated information from professionals of local authorities and ministries, private companies, others organizations… any relevant actors and informant of the sector, in order to confirm and refine collected and analysed information (i.e. geology, hydrology, yield of wells and boreholes, water quality).
Hydro-geophysical methodologies These methodologies don’t replace the steps described above. Even in some cases, the information collected through mapping and discussions with local professionals is enough to locate properly the sitting for the borehole or the well.
Electrical resistivity method: a direct current flow is fed into the ground and the resistivity of the formations is calculated from the measured potential differences. The variations of the resistivity allow you to describe the nature and structure of the aquifers. Wide range of applications.
Electromagnetic method: uses electromagnetic waves through time-varying currents to measure the conductivity of the formations. Easier to use than the electrical resistivity.
Magnetic resonance sounding: it gives direct information on the presence of groundwater, measuring spin and magnetic moment of the hydrogen nucleus. Difficult to use.
These different steps for the borehole prospecting are more detailed in the Action Against Hunger book: ACTION CONTRE LA FAIM, 2005. Water, sanitation and hygiene for populations at risk. 2nd edition. Paris : Hermann. Also available at https://www.ircwash.org/sites/default/files/acf-2005-water.pdf
You have here a wide range of different products, most of them being household water treatment (HHWT) solutions that could be used during emergency responses, when sources of potable water are not ...(read full answer)
You have here a wide range of different products, most of them being household water treatment (HHWT) solutions that could be used during emergency responses, when sources of potable water are not available; but one – from Water Makers – being a reverse osmosis desalinization system.
Then the choice depends on your objectives:
Why do you want to treat water? What are the available sources of drinking water? How many people are affected? After the emergency response – during which portable water treatment kits could be used, what longer term solution are you planning for drinking water? What is your budget available? And finally, which system/technology would be accepted by the users?
Firstly, before making any choice, keep in mind that the chlorine, when properly used and dosed, has, what we call a “persistent effect”: you always add a little bit more of chlorine than needed, to make sure that you have some free residual chlorine in your water.
During emergency response, when people might be exposed to diseases or outbreak and/or when hygienic practices of people are not healthy, the drinking water could be re-contaminated after treatment – i.e. through dirty hands or buckets. So, even if the water has been filtered using Waves for Water or Sawyer filters, it could be contaminated afterwards, through risky hygienic practices. Thus, purification tablets/chlorine tablets (supplied with the Dayone response water bag and by the internationally known Aquatabs offering a wide range of products) would properly treat your water and a remaining/extra quantity of chlorine present – called “residual chlorine” – in the treated water would prevent opportunistic re-contaminations.
Even if you’re working in an environment where the hygienic practices seem to be good, I would recommend the use of chlorine for the treatment of water, which could be combined to the filtration: first, filter the water (which will remove lots of contaminants and suspended matters) and then disinfect it (the filtration would reduce the quantity of chlorine required to treat the water) making sure that you’ll have “free residual chlorine” after treatment.
Of course, if you’re looking for a system that you may use during your treks in the pristine mountains, you can use the filter bags without chlorine to filter the water from the torrents!
Cost and time
Remember that if you plan to distribute massively HHWT technologies, you’ll need to properly train the users and monitor the use. Then, when you target a large number of affected population, it will be more expensive to organize a distribution of HHWT technologies than to protect and use a source of good quality water. But during an emergency response, it could be the only solution; which should be a temporary solution.
Chlorination at the points of use
Under extreme conditions, you may need to set up water treatment at the point of use. It’s quite common during cholera/Ebola outbreak. You’ll set up different chlorination points which consist of some trained technicians chlorinating the collected water directly into the buckets carried by the users. The chlorination points could be at the water source/water point or distributed strategically in several locations, visible by the users. This could be an efficient temporary solution, but time and money consuming.
Finally, have a look at your budget constraints and ordering/delivering procedures to select the most appropriate technology. I don’t know where you’re working and under which conditions, but importing these filter bags might take time and money; while chlorine may be more easily accessible locally or in the region. And there are DIY ways of filtering water.
Have a look to these Factsheets from WEDC, WHO and the International Federation of the Red Cross and Red Crescent on the HHWT techniques:
Desalinization of water Looking at the Water Makers technology, this is something completely different. This is a technology to desalinate the sea water. The reverse osmosis (RO) is quite efficient to treat the sea water and could be useful when fresh water is not available or contaminated. But the RO requires huge amount of energy and it could be more expense than protecting/rehabilitating/improving existing fresh water sources.
Again, I would then consider the different options available:
What are the existing sources of drinking water? Are the hygienic practices safe? Are there any risks of diseases outbreak? What are the local practices in terms of household water treatment? What are the locally available technologies/systems? What is acceptable by the users (the use of the system and the taste of water)? What is the budget available? What is my timeframe? …
I hope it was useful.
We always used the Abney level in Laos to conduct topographic surveys in the mountains, hills and forest, from the spring down to the village. With a relatively small team and with limited material...(read full answer)
We always used the Abney level in Laos to conduct topographic surveys in the mountains, hills and forest, from the spring down to the village. With a relatively small team and with limited materials, you can easily collect the data to draw the topographic profile; in order to estimate the hydraulic feasibility and to design your gravity fed system (GFS).
A clinometer? For what?
To draw a topographic profile between 2 points, you need to know the distance at ground level and the vertical distance (or difference of altitudes) between these 2 points. You can easily measure the distance at ground level – called L – with a measuring tape. But the difference of altitude – called ΔH – can be calculated if you know the inclination angle – called α – between these 2 points and remembering your trigonometry lessons. Your Abney level measures this angle. Sinus α = ΔH/L
- 1 clinometer Abney level.
- 1 30m measuring tape.
- 2 wooden or bamboo stick of the same length. The extremity of the sticks is marked with red scotch tape.
- Red spray (to mark the road followed).
- Field sheet (to collect data).
- 1 person for Station 0 (measuring vertical angle and horizontal distance).
- 1 person for Station 1.
- 1 person for data collection.
- Village’s volunteers to guide the team to the springs, to clear the way, to prepare the short wooden stick (to mark the stations)…
- Preparation of equipment and tools.
- To define Station 0 (starting point of the survey).
- To define Station 1 on a low or high point of the topography and visible from Station 0.
- To measure the soil distance (L) between Station 0 and Station 1 (using the measuring tape).
- To target the extremity of Station 1 from the extremity of Station 0 using the Abney level.
- The Stations 0 and 1 are marked with short wooden sticks hammered in the soil. On these short sticks are written the number corresponding to the Station and the distance; in addition the nearest rock or tree from the Station is marked using the red spray
- Once the 2 parameters are measured (horizontal distance and vertical angle) and the 2 Stations are marked, the Station 0 stick is moved – with the clinometer – to the Station 1 and the Station 2 has to be defined.
For the topographic survey, the shortest way to the village has to be followed and showed/cleared by the villagers. However, huge slopes have to be avoided as well as river’s bed.
After Irma and María hurricanes, some islands of the Caribbean experienced blackout and water-supply cut-off for several weeks or months. In Puerto Rico for instance, severely hit by hurricane Marí...(read full answer)
After Irma and María hurricanes, some islands of the Caribbean experienced blackout and water-supply cut-off for several weeks or months. In Puerto Rico for instance, severely hit by hurricane María, there was no mechanism of disaster preparedness or mitigation. The piped water system was the exclusive source of drinking water and people have been (and some are still) exposed to cut-off. Then, the alternative sources of water may be bottled water – which is not environmentally and economically sustainable – or any others water resources available such as springs, wells, surface water (i.e. creeks, rivers and ponds) or rain water; inhabitants are then exposed to risk of water and hygiene related infections and diseases.
In Puerto Rico, the emergency responses for water were:
Massive distribution of bottled water, brought from the USA. Problem of solid wastes management with all these plastic bottles, where there’s no recycling practices or plants on the island. And when all the bottles are empty, where the people will get their water from?
Distribution of household water filter, brought from the USA.
Water trucking (of piped water), but even the national authorities recommended the people to treat this water before drinking it (filtration, boiling or disinfection).
Alternative water sources: many rely on unprotected water sources; the natural disaster generated landslides and floods (and flooded sceptic tanks and sewage systems) contaminating springs, wells and surface waters. However, these solutions are temporary and in case of new natural disaster, the inhabitants would end up in the same situation, without access to good quality water.
Water and Disaster Risk Reduction (DRR)
A longer-term solution could be the design of durable and ambitious community led programs, aiming at building the disaster resilience and preparedness of communities. Under the umbrella of DRR (and Climate Change Adaptation), you could develop some of the following activities:
Water safety plan: in order to select the water resources with the best quality and to protect these water resources from contamination:
o Water quality analysis and monitoring (of the existing water resources such as piped water system, spring, river, well and rain)
o Protection of the water resources from the source to the use/consumption until the management of waste waters (such as environmental management, protection of the watershed, organic and disaster-resistant agriculture, reutilization of grey water, composting toilets).
Promotion and training on decentralized and disaster-resistant water supply system, at community and/or individual levels:
o Repair/rehabilitation/improvement of existing community decentralized water supply systems;
o And/or rain water harvesting community and/or individual systems with filtration units.
Campaigns of environmental health education, hygiene promotion, DRR and CCA, in order to promote the use of decentralized water supply system and the protection of water resources.
DRR trainings and mitigation measures (i.e. alerts, communication, disaster-resistant house, food stock, water supply, energy, etc.).
Support for the most vulnerable (criteria to be defined, such as elders, disabled, single headed families, etc.) through:
o And/or manpower;
o And/or familial and adapted decentralized water supply system.
Education for schools’ pupils and students: on environmental health, DRR, CCA, water quality, etc.