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Help with rainwater test results


can anyone help me? I am doing a project on rainwater harvesting and I have a sample of rainwater to be analysed in a laboratory. I would like to know more about the results obtained, whether it is in the acceptable range.

Here are the results:

Phosphate: 3.34 mol/dm3

Nitrite: 0

Nitrate: 2.26 mol/dm3

I would also like to know if I can use the rainwater for bathing.



1. Rain water usage

Rain water is being used in all fields from medical to irrgation of agricultural fields depending upon the method of collection and equipment used and also the procedure of treatment before use. That is a pure rain water and is called pure water. When it is mixed with other pollutant water stream sometimes it becomes black water. Bathing with rain water is not bad if you directly bathe in the rain though initial rains sometimes carry acidic properties as well.

2. Rooftop rainwater harvesting


In fact the rainwater is to be collected on rooftops of buildings. The rooftop is actually made up of a mixture of tar & gravel. From the laboratory test I could only obtain results for nitrite, nitrate and phosphate and I would like to know if the results obtained is favorable to the use of the rainwater for bathing.

Phosphate: 3.34 mol/dm3
Nitrite: 0
Nitrate: 2.26 mol/dm3

Through some research I found that the TSS(Total Suspended Solids) analysis was a way of analysing the water quality but I would like to know about the acceptable range for bathing purposes.


3. Various environmental

Various environmental protection agencies including ,WHO & health agencies of different countries have different standards for bathing water but they mostly consider presence of bacteria and other living organisms (like coliform, bacili, etc) objectionable.

The total dissolved or suspended solids does not make much difference as people take bath in sea water as well. Hence there is no such limit prescribed by these agencies. Since you will be collecting the water from building roof-tops it will be having less suspended solids after first or second drain, and if the roof-top is regularly cleaned up.

4. Fiber reinforced plastic roof top RWH

Dear Experts,

We are in Bangalore and have decided to implement rain water harvesting in our apartment. While doing the feasibility study, we found major part of the area is covered with glass fiber reinforced plastic (FRP) roof sheet.

My questions are

1. Can we include the FRP sheet covered area for RWH? Is there any chances of water contamination because of FRP sheet?
2. Can we use the rain water directly (bathing, cooking) with necessary filters? What type of filters are required?

Please advise.FRP shade

Dhanasekar D

5. Go for in-line pipe treatment units


I am Mr. Aditya Aphale. I am doing M.Tech (Environmental) at Walchand College of engineering, Sangli in Maharashtra. I am currently working in project phase. My project topic is "Studies on quality and treatment of rooftop harvested rainwater in Sangli".

During my preliminary study, I have carried out characterization of rooftop harvested rainwater. I have analyzed various parameters like pH, turbidity, conductivity, hardness, chlorides, nitrates, acidity, alkalinity, heavy metals like Pb, Zn, Cd, Cu, Cr, As, Ca, Mg, Mn, Fe, etc and trace elements like Na, K, Ba, Ni, etc. Out of all these parameters turbidity and heavy metals are of mainly concerned regarding quality issue. If harvested rainwater want to use for any utility purpose, it is necessary to install treatment units for the removal of various contaminants.

Now, regarding FRP roof, due to FRP roof, the rainwater precipitating on the roof may get contaminated with various contaminants like heavy metals and other minor/trace elements. Because I have gone through various literature review, and various studies have been conducted on effect of FRP roofs on the quality of rooftop harvested rainwater. These all studies concludes that there is contamination of heavy metals and trace elements in harvested rainwater. the contamination of these heavy metals and other elements mainly depends upon atmospheric pollutants present surrounding that area, if rain occurs during highly polluted atmospheric conditions, rainwater washes out the atmospheric pollutants and get contaminated. So, this water is get contaminated heavily with heavy metals and dust particles.

So this harvested rainwater should be treated and can be used for daily utility activities like Bathing, Cooking, washing, etc. The roof surface doesn't play that much role in contamination of rainwater, as rainwater is getting contaminated due to other atmospheric conditions. But FRP roofs can show various leaching actions when get contact with rainwater, means various trace particles/contaminants can get leached from FRP roofs, can contaminate water.

So it is better to treat the harvested water when it is being used for utility purposes like bathing, cooking, washing, etc.

There are various types of in-line pipe treatment units like in-line pipe filters for RWH. But those filters are having lot of drawbacks such as, they are less efficient in removing contaminants like heavy metals, they can remove the turbidity, but the efficiency is also less.

There can be one another option for treatment, that, harvested rainwater can be collected first and treated separately and stored. But separate treatment systems may be costly than in-line pipe treatment units. So, it is better to go for in-line pipe treatment units.

6. Is there relevant documentation for claim regarding FRP roofs?

Dear Mr.Aphale

You mention that rainwater harvested from FRP roofs will contain heavy metals. How can they originate from the FRP roof? May I know the sources from which you got this information?

They cannot come from the fiberglass per se. If they are to come from the pollutants in the air, dissolved by the rainwater, the area involved must be a heavy industrialized place.

Are you saying that you have found heavy metals in the rooftop rainwater in Sangli? We can avoid sweeping generalizations that are not backed by relevant documentation that will create unnecessary doubts and concerns amongst people.

Indukanth Ragade

7. Have a small cemented pit through which the rainwater passes

Dear Mr.Shanasekar

I notice that the FRP foof is is not a flat one but a curved one. In such cases where there of cannot be physically accessed and swept clean before the monsoon sets in, what can be done is to introduce a first flush arrangement whereby the dust or leaves coming with the water in the first rain can be prevented from going into the sump or the well. This can be just a drum with an inlet going from the top to the bottom and an outlet at the top. The drum has to be emptied after the first rain. Alternatively, you can have a small cemented pit through which the rainwater passes and have a grill at the outlet. After the first rain, the pit is cleaned free of mud and leaves.

Indukanth Ragade

8. Fibre reinforced roof top RWH-No problem in using the water

There is no problem in using the water from such a roof for bathing and washing of clothes. It is better to sweep the roof (cemented or of FRP) before the rains.The water can be used for cooking after filtering through cloth. The water can be used for drinking also after filtering, boiling and cooling.

Indukanth Ragade(

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