Rainwater Harvest

Hello everyone, how are you? For those who have just started to read this blog, it's all about what option or steps that you can take to use energy efficiently at your home or your office. So how is the weather out there? Now that the El Nino has strike, many areas are being flooded by the rainstorm. So I was thinking, with so much of rain, is there any ways to reuse the rain water? I'd found out that there is such a way and it's called Rainwater Harvesting.

What is Rainwater Harvesting?

We have many rainy seasons especially in South East Asia but how does rain happen? In order for it to rain, the air must be saturated: The relative humidity must be 100 percent, or very close to it. How does that happen? By lowering the temperature or bringing in more water vapor. But if we just bring in more water vapor and nothing else happens, we're still just stuck with microscopic droplets. So let's focus on lowering the temperature. The temperature can be lowered by a colder wind, possibly coming from the north. But those north winds contain less water vapor, so the temperature may lower, but the humidity could remain the same.

So since we are having rains for almost half of the year, we should make use of it. We call this as rainwater harvesting. It is the accumulation and deposition of rainwater for reuse on-site, rather than allowing it to run off. Its uses include water for garden, water for livestock, water for irrigation, water for domestic use with proper treatment, and indoor heating for houses etc. In many places, the water collected is just redirected to a deep pit with percolation. The harvested water can be used as drinking water as well as for storage and other purpose like irrigation.

Rainwater harvesting provides an independent water supply during regional water restrictions and in developed countries is often used to supplement the main supply. It provides water when there is a drought, can help mitigate flooding of low-lying areas, and reduces demand on wells which may enable ground water levels to be sustained. It also helps in the availability of potable water as rainwater is substantially free of salinity and other salts.

How to Design It?

There are many technologies in the market that can be used in the rainwater harvesting process.  The rainwater can be collected from virtually any surface, but yet bare rooftops generally yield the best quality rainwater with the least treatment. Not all of the rainwater that strikes a roof can be collected: water is lost from evaporation, blowing wind, overflowing gutters, and leaky collection pipes, first-flush devices, and self-cleaning filters. 

On average, Asians use 70 gallons per person per day to operate toilets, showers, clothes-washers, sinks, and other water-using fixtures and appliances. By replacing fixtures and appliances with modern water-efficient versions and repairing leaks, water usage can be reduced to less than 50 gallons per person per day. 

The most appropriately sized rainwater storage can be chosen by quantitatively assessing the performance of various sized storage capacities. By assessing the performance of various sized storage capacities, it is possible to make an informed decision as to what would be the most suitably sized storage capacity for the given application. The input for the assessment is historical daily rainfall data, and the performance of a particular storage capacity can be judged by how much water is required to be supplied from other sources to makeup for any shortfall in demand.

One of the ways to collect rainwater is the RainSaucer. Instead of using the roof for catchment, the RainSaucer, which looks like an upside down umbrella, collects rain straight from the sky. This decreases the potential for contamination and makes potable water for developing countries a potential application. Other applications of this free standing rainwater collection approach are sustainable gardening and small plot farming.

Pros & Cons

Every technology out there will surely have its own upsides and downsides. The rainwater harvesting is not excluded. So I'll share what are the pros and cons of this rainwater harvesting.

Upsides:

• Collection, storage and usage of rainwater helps to relieve pressure on the domestic water supply. Therefore, the environment from where it is extracted has positive impact on the water catchments by reducing the impact on the ecological water reserve.
• Provides clean water sources, especially in urban areas for a wide variety of uses.
• Saves money on the water bill.
• No pump is required, therefore no energy is needed.
• Water from the harvest contains less chlorine and other chemicals used in water treatment, so there is less chance of chemical build-up in soils.
• Water from the harvest is softer due to fewer additives, such as limescale, therefore it's better for laundry in hard water areas.
• It decreases urban flooding.

Cons:

• Rainwater contains small traces of bird and animal faeces, dust, mosses, lichens, pollution particulates, dissolved gasses and other airborne ions, thus filtration and purification may be needed of water is to be used for consumption.
• Rainwater harvest installation is quite a tedious work.
• Requires space and may detract aesthetic value.
• The water from the harvest is sometimes not suitable for drinking.
• Rainfall is often seasonal, which means there is still reliance on domestic water supply.
• The initial cost for tanks and pipings are costly.

Financial Analysis

Calculating the cost of a setting up a rainwater harvesting system can be difficult as it depends on a range of factors apart from the initial outlay for the tank and pump system. If you are retrofitting to an old build this can also include:

• The cost of putting in the new conduit or piping to feed utilities like the toilet or washing machine.

• Shaping water collection from your roof with new guttering that feeds into your rainwater harvesting tank.

• Excavating the area outside your property if you are planning to have the water tank underground.

It will cost Malaysians between RM1,500 and RM10,000 to install a rainwater harvesting system to guarantee uninterrupted water supply in their homes and office buildings when taps run dry. An expert said the cost depended on the tank size, the installation location (under the roof or front yard or the balcony) and the usage of pump and filter for the system. Most people do not install the rain water harvesting (RWH) system because they think it would be very expensive and would require a lot of space.

The rainwater harvesting and recycling systems implemented successfully in several countries, including Australia and India. The retention, collection and reuse of rain water as well as diverting of river water into nearby ponds should be a focus to ensure that the country do not face a water crisis in the future. Housing estates should also be equipped with rainwater harvesting systems to reduce the use of treated water. The expert said RWH systems are environmentally sound and can help reduce public demand for water from water concessionaires.

Whilst installing a rainwater harvesting system to reduce your mains usage has a number of advantages, you can also save a lot of money and reduce costs by taking a more holistic approach to your daily consumption. These can include:

• Install a low flush toilet or put a plastic bottle filled with water into your cistern (reducing the amount of water it fills with). An average flush of a toilet uses around 13 litres of water each time you pull that handle.
• When you brush your teeth, don’t leave the water running. It sounds like a simple thing to do but many people waste water by letting the tap run for a whole two minutes while they polish those dentures.
• Buy a water efficient washing machine or dishwasher and only use when there is a full load, using the economy setting.
• If you have dripping taps then make the effort to buy new washers and mend them – it may not seem a lot but over a year can make you savings.