Rain Water Harvesting System Design Project Course faculty: Prof. Gaurang Shah Shyamali Verma, 8th Semester, Product Design
What is Rain-water harvesting? It is a direct collection of rain water. It involves cleaning the collected water for it to be stored and used immediately or directing it so that it percolates into the ground to recharge the ground water table and may be used later through bore wells.
Why do we need to harvest rain water? 80% of the earth’s surface is covered with water yet only 1% of that is Freshwater. The rest is Sea water or Ice locked up in the Polar Regions or snow in the mountains. The population in urban areas is growing rapidly. So also is their water needs, fuelled by changing lifestyles. Large urban populations are supported by cleaning and transporting water from great distances and at great expense, to the city. As centralized supply of piped water has remained limited, we have turned to the next source – groundwater, to supplement our consumption. Groundwater is extracted from bore wells or reaches homes through water tankers. This is lowering the water table level under us. As the water in the soil goes down the water from the seas tends to come in (ingress). Sea water is makes the land and the remaining water saline. We generally receive rain in heavy showers followed by dry sells. When it rains heavily the soil is not able to absorb the water at the rate of rainfall. As a result most of the rain drains away into the seas/ rivers, causing soil erosion or causes flooding.
Other advantages: Rain water is a free source of water which is relatively easier to clean and since it can be used where it is collected cost of transporting water is not there. Installing a rainwater harvesting system is not only simple; it is a onetime cost that will be recovered in 2-3 years. Move towards sustainability. No situation of “water, water everywhere and not a drop to drink” in the monsoon months.
How is it done? There are many methods that may be employed to harvest rain water depending on the location. Some of them are listed below. 1. Rooftop collection 2. Bore well recharge 3. Percolation pits, trenches.
Who installs these systems? There are various contractors in cities that come and evaluate the area/ location free of charge and then plan the system and get it installed within a week’s time.
In urban settings: A Rooftop Rainwater harvesting system fits best in the urban areas. There are four major components of a Rooftop RWH system. 1. 2. 3. 4.
Catchment/ capture area Conveyance system Filtering device Collection device or Percolation pit
1. Catchment area: The rooftop/ terrace acts as the catchment. There is a gentle slope given to a terrace which directs water to an outlet taking the water down (downspout) which normally mixes with the drainage of the building or is let out at ground level. One needs to tap this water. The roof water can be directed from the downspout to a storage tank or a filtration device. For this one must first ensure that the roof is cleaned thoroughly before the first showers are expected so as to remove leaves, bird dropping, etc. Also during the monsoon season the roof mustn’t be used at all.
2. Conveyance system: Conveyance systems are required to transfer the rainwater flowing from the rooftops to the storage area. The existing downspouts are adequate for this the only modification required is to connect up all the downspouts to direct the rainwater to a designated area. It has to be seen to that the first few liters of water are not collected since the rain water cleans out all the dust settled on the terrace/ roof as well as in the pipes. This is known as first flush.
3. Filtration system: While rainwater is one of the purest forms of water, it needs to be filtered of any rooftop contaminants. The filter is inexpensive and is assembled in a drum with 3 layers consisting of gravel stones at the bottom, brick pieces above that and fine sand on top. Sometimes charcoal is also added. Rainwater is directed from the top and after filtering through the layers is drained out from the bottom.
4. Collection devices: Depending on whether one intends to store the water and use it or whether one wishes to direct the rainwater underground, the following are used. Storage tanks are used either above or below the ground. One can either use a Plastic (sintex) tank or have a concrete tank constructed. Cost: a sintex tank normally costs Rs 2 per litre. a concrete tank is usually between Rs 5 to Rs 7 per little.
Percolation pits are used to hasten the penetration of water into the underground aquifers. It is as simple as a trench of 1 meter width and 1 meter in depth. The sides of the trench are cemented but the floor is left as it is. With gravity water infiltrates and reaches the aquifers. When using a percolation pit the sand filters is combined with the pit. This pit can be covered with perforated concrete blocks or a wire mesh so as to prevent things and people from falling into it. Cost: perforated concrete slabs cost Rs 250 per sq. meter.
In suburban settings: A bore well recharge system works brilliantly in places where bore wells run dry frequently and ground water is the only source of water.
This system is installed in 5 steps: Step 1: A percolation pit of 10 ft. diameter and 10 ft deep is market around the bore well and dug out with the help of an earth mover and manual labor.
Step 2: Tiny 7mm holes are made in the underground boring tube.
Step 3: The tube is then wrapped with food grade stainless steel wire mesh which acts as a filter.
Step 4: The percolation pit is filled with sand and gravel and the land is leveled again.
Step 5: A concrete platform may be constructed around the bore well so as to assist people in reaching it and filling water. So when it rains the gravel and sand filled pit allows percolation of rain water into the aquifer which the bore well is tapping water from.The holes in the boring pipe allow the rainwater to go directly into the boring tube. With this process a bore helps all the other bore wells in the area get water for the monsoon months. Further if other bore wells in the area are also worked on then a bore well may become perennial in just 2 years.
Mit Institute Of Design Campus The effort was to study the MIT id campus and propose a rain water harvesting system.
In the institute: Where does the water come from? Into the institute and the campus in general, the water comes from a well in Raiwadi, about 5 kilometers from the campus down the Pune – Solapur highway. From there it goes directly to the institute filtration plant where it gets chlorinated and is sent back to the Gurukul and Manet pressure plant. Before that two inlets are directed to the hostel building and the institute building. Besides the well at Raiwadi a bore well a little behind the hostel also supplies water to the hostel. Some water from it is also let into the well behind the hostel building. Here the hard water from the bore well mixes with the soft water of the well, and from there water is again directed again towards the Gurukul and Manet pressure plant. For gardening and construction work, water from the river is pumped into the well in front of the hostel from which one pump sends water for gardening and another pump sends water to the field behind the cowshed.
Water movement on the campus
From Raiwadi well Raiwadi - filtered From Bore well Bore well- mixed From River
Well at Raiwadi
Filteration plant
Well in front of the hostel building
Well beside the hostel building
How is it distributed? Hostel: The plumbing for the hostel building is divides into two parts, the river side and the field side. Behind the hostel there are two sintex tanks of the capacity of 10,000 liters each supplying water to one side of the hostel building. The water for these tanks is supplied by both the well water from Raiwadi and the bore well. The water from both sources gets mixed in these tanks. It is the pumped around 4-6 times a day to tanks above the building. There are 3 cold water tanks and 1 solar water tank on each side of the hostel, each with the capacity of 5000 liters. Pumps used: for pumping water from tanks at the bottom to tanks on the terrace, two pumps of 3 hp each are used.
Institute building: The plumbing for the institute building is also divided into 2 parts just like the hostel building. Behind the institute building, there are 3 half in-half out sintex tanks of the capacity of 5000 liters each. These tanks are supplied water only by the Raiwadi well. Above the building there are a total of 3 tanks of capacity 300 liters each, of which 2 are on the men’s washroom side and 1 on the ladies washroom side. These too are refilled about 4 times a day. Pumps used: for pumping water from tanks at the bottom to tanks on the terrace two pumps of 1 ½ hp and one pump of 1 hp are used.
Clean water pipes Raiwdi – filtered From Bore well Rain water pipes Sewage pipes
Water tanks
Underground sewage pipe Underground sewage pipe
All the rain water drains away along with the waste into the septic tank, goes onto the lawns or flows into the river.
Institute building tanks (5,000 lt. each)
Hostel building tanks (10,000 lt. each)
Tanks on the institute building terrace(3,000 lt. each)
Hostel building tank with inlet pipes and pump
Drainage: Pipes, from both the terrace and the washrooms, in both buildings, come down go into a septic tank beside the institute. Other downspouts (7 in number) go from every floor and open out on the ground floor. Five of them open out on the lawns while two open on the other side, onto the ground sloping towards the river. So as of now all the rain water drains away along with the waste into the septic tank, goes onto the lawns or flows into the river.
Consumption: The average consumption per person generally is taken to be 200 liters per day; hence with about 600 people on campus the total consumption comes to 120,000 liters a day. Terrace area available: The area of the institute is about 3456 sq meters while that of the hostel building is around 1444 sq meters. Amount of rainwater draining away: Average rainfall in Pune: 722 mm Water collected by the institute terrace: 2495 cubic meters. About 2,000,000 liters per year, that makes about 5000 liters per day. Water collected by the hostel terrace: 1042 cubic meters. About 1,000,000 liters per year, that makes about 2000 liters per day.
Front View
Side View
Water tanks
Underground sewage pipe Underground sewage pipe
Drainage pipes coming from each floor
Drainage pipes opening in the lawns
Underground sewage tanks
Drainage pipes going underground leading to Sewage tank
The idea is to collect water on both terraces and then filter it and then to let it into a syntax tank up to a certain amount, and the rest to go back into the bore well. In the process to manage water in such a way so that the water from the institute may be diverted to the hostel, since the water consumption in the hostel is more and the institute collects more water due to its area (3456 sq meters of institute terrace area against 1444 sq meters of hostel terrace area).
Amount of rainfall collecting per day(24 hrs) On an average the maximum rainfall received on a single day would be 6cm Therefore the maximum amount of rainfall collecting on the rooftop per day is: Institute terrace: 3000sq. Meters. Rain collected: 180 cubic meters= 1,80,000 lt. Hostel terrace: 1000 sq meters. Rain collected: 60 cubic meters= 60,000 lt.
Top View – Institute building Drainage pipes
All the down-spouts on the terrace are to be connected and led to the hostel side of the institute where the water tanks are located. In this way all the water gets divided into two parts on either side of the building.
Drainage outlets on institute terrace
Water tanks
Water tanks
Front View - Institute Building Drainage pipes from terrace
Drainage pipes from other floors
Also it is to be seen that the terrace downspouts are separated from the other floors. Since that water cannot be used. The common collector pipe has to be given a gentle slope. Also, while the rainwater is travelling downwards , a filter is to be put in its way.
The rain water collected from the right side of the building is sent to the rightmost water tank .
Side View Water tanks
The overflow from this tank is sent to the middle tank. While the water collected from the left side of the building is sent to the leftmost water tank. A similar treatment is given to the hostel building.
Clean water pipes Raiwdi – filtered Rain water pipes
All the rain water collected from the college building is first sent to the college tanks. The overflow from these tanks is then pumped into the hostel tanks. Here it gets combined with the hostel rain water. Any overflow from the hostel tanks will flow to the bore well and is let to percolate into the ground either by the bore well recharge method or by digging a percolation pit.
Top View – MIT Institute of design campus Bore Well/ Percolation pit
Well
Water tanks
Water tanks Rain water pipes