Everything You Need to Know About the Rainwater Harvesting Process

Let us face the hard truth. India receives a huge rainfall, and over 70% of this water runs off our roofs and streams. On the other hand, millions of people across our villages and cities face acute water shortage due to groundwater depletion. That should perhaps explain the very irony that exists in our own land. How about a situation where your roof serves as a perfect means to help you save water and reduce water scarcity? Well, that is where Rainwater Harvesting comes to the core. It is not only about saving water. The process is a great means for decentralised water management. With proper rainwater harvesting, you can be independent from the municipal water supply woes. You are empowering your own home for capturing, storing, and using the water. This blog is an attempt to help you understand the entire rainwater harvesting system and how to make the best of it.

The Core Principle & Calculation

So, what are the core principles of a rainwater harvesting system? Well, the entire system is based on GRAVITY. Contrary to several other technologies, rainwater harvesting is not about some sort of complex and energy-intensive process. The core functionality remains simple and completely natural. Water falls from the sky, you guide it through the slopes and pipes downward, and then it is either stored or percolates into the ground. You need no electricity, no pumps, or no electricity bills. The end result? Even the modest of roofs can help you generate an enormous amount of water! Want an estimate of the potential of rainwater harvesting? Here is the perfect example – Formula = Roof Area (sq. m) × Annual Rainfall (mm) × Runoff Coefficient (0.8-0.9) = Annual Water Potential (liters) Let us imagine a roof size of 1000 sq.ft. Assuming a moderate rainfall of 800 mm, the total water collected would be 70000 litres per year. If you consider high rainfall regions, this can reach an enormous water collection of 100,000 litres or even more.

Phase 1: Collection (Catchment & Conveyance)

The collection of catchment is the first part of a rainwater harvesting system. The roof is called the Catchment Surface. Suitable surfaces  The concrete or RCC roofs are the best and considered to be the gold standard for rainwater harvesting. Galvanised Iron roofs can also offer a better runoff. Even the tiles can work great if maintained well enough. However, we recommend avoiding roofs with chemical coating, asbestos sheets, or roofs covered with excessive moss. Gutters and Channels  The UPVC gutters can be considered to be the veins of the system. They guide water from every corner of your roof to your downspouts. Gutters should have a proper sloping. Otherwise, they may become a breeding ground for mosquitoes. Gutters should be designed with a gentle slope. Experts claim that a 1% taper is the best option. The materials used for the downspouts should ideally be Hysquare Pipe and Fittings. PVC is affordable, while aluminium lasts longer. Downspouts These are the vertical pipes that carry water from the gutters to the storage or recharge system. The sizing of the pipes matters a lot here. An undersized downspout may result in backup in heavy rainfall. A simple and ideal rule should be to use a minimum 4-inch pipe for every 1000 sq feet of roof area. If your downspout is too narrow, you may end up with an overflow.

Phase 2 – Protection

The phase includes First Flush. If you are relying on a DIY method for rainwater harvesting, this is where most of such systems fail. Many DIY systems skip this phase. This can make the collected water murky and taste odd. The first rain of water is always filthy. It might be carrying an enormous amount of dust, bird droppings, and whatnot. The First Flush Diverter is your system's "gatekeeper." It segregates the initial dirty water from the clean flow that follows. Most first flush diverters work on a simple principle: a T-junction or chamber that diverts water down a separate pipe for the first few minutes of rainfall. Once the water running off your roof is clean (which happens surprisingly fast—usually within 5-10 minutes of rain), you manually or automatically switch the flow to your main tank. You should divert around 1 to 2 mm of the initial rainfall. If you have a 1000 sq feet roof, you should divert around 60 litres of water.

Phase 3 – Filtration

Even after the First Flush, the water is not yet pure. The next step filters out the remaining sediment, algae spores, and fine particles. The filtration system involves several sections.

• Mesh filters – They act as leaf traps. These can trap larger debris. These include leaves, twigs, and such other elements. You should clean these mesh traps regularly.
• Main filter – You can choose among traditional filters and modern filters. If feasible, you can consider using a hybrid filter.

Traditional filters have a layered approach that uses gravel on the bottom, sand in the middle, and activated charcoal on top. However, they would need regular maintenance. Modern filters work on the principle of centrifugal force. They are compact and need less maintenance. However, they need more space. Most of the Indian homes work great with a hybrid approach.

Phase 4 – Storage vs recharge

This is the last phase where the collected water splits into tow paths. You would either store it for immediate usage or you can use it for recharging your groundwater system. Direct Use  In this method, the filtered water drops into a sump or underground tank. This works as your personal water reservoir. The water so collected can be used for multiple purposes –

• Toilet flushing
• Gardening and landscaping
• Washing cars and outdoor cleaning
• Potentially drinking water (with additional treatment)

However, the water thus collected may not be suitable for drinking. It may be susceptible to contamination. We recommend using airtight lids and even UV filters for safety. Groundwater recharge  When your storage is full or when your purpose is to recharge your groundwater table, this should be the best option. There are several options that can go handy in this context.

• Recharge pits – They are quite simple. Just dig a trench and fill it with layers of large rocks at the bottom and smaller gravels in the middle. Feed your filtered rainwater into this pit. It will percolate through the soil and reaches the groundwater table.
• Borewell recharge – This is best suited for dry or low yielding borewells. You can feed the collected rainwater directly into the borewell casing. It will then recharge the aquifer around the well.

We consider groundwater recharge is often better than storage. You're solving the problem at the source—reviving the aquifer—instead of just postponing the problem by storing a few thousand liters.

Maintenance

Well, the maintenance stage is non-negotiable. No matter how impeccable the system is, it will fail without proper maintenance shortly. Here are a few maintenance steps that should be extremely practical – Pre-monsoon (April-May) Sweep off all the dust from the roof. Remove the dead leaves, and everything else that needs to be removed. Clean the gutters thoroughly. Check the downspouts for any sort of blockage. Test the First Flush Diverter. During Monsoon (June-September) After every rainfall that is significant, drain the First Flush pipe. Flush out the water. This should help you prevent the sediment buildup inside the filter. Also check the leaf traps after a heavy rain. Post-Monsoon (October-November) The maintenance would typically depend on the filters you are using. De-silt the sand filter if you are using traditional filters. Clean any dust on your main filter. Check the entire tank for any sort of sediment accumulation and siphon it off completely. Drain any stagnant water from your gutters and downspouts before the dry season sets in.

Conclusion

If you are environmentally conscious, rainwater harvesting is not something you will consider a fad or luxury. It is an investment in the right direction and should be the right step in fighting the water crisis in India. However, we strongly recommend not opting for the DIY techniques when installing or maintaining the rainwater harvesting system in your premises. Partnering with professional service providers like EuroGuard can come quite handy. And the money? A modest 1000 sq. ft. system costs between 50,000 to 100,000 rupees to install. If it saves you even 5,000 rupees monthly in tanker costs and electricity (from not running deeper borewells), it pays for itself in under two years. After that, it's pure savings.