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How Rainwater Quality 'Compares' and Water Treatment Specialists Can Make It Even Better

By Scott O. Shaffer

Part Two of Three

Just how much better 'is' rainwater?

Research conducted during the past two years by Environmental Laboratory Services/LCRA and Texas Water Savers Co. suggests the quality of untreated cistern-stored rainwater far exceeds EPA drinking water standards. Treatment only stands to make it that much better.

The rainharvest systems reported on in this article used metal and composite roofs. Some systems included gutter screens and filters and others did not. Some used disinfecting equipment while others didn't. The amounts of aluminum, copper, chloride, iron, lead, nitrate, sulfate, zinc, odor (and hardness) in the rainwater samples was far less than reported by Austin, San Antonio and Houston (see Table 1).

Legislation passed during the 82nd Texas Legislature (HB 3372, HB 3391 and SB 1073) supports installation and maintenance of rainwater harvesting systems that are used for indoor potable purposes and connected to a public water supply system. Several organizations are drafting regulations to guide city building departments as they permit these systems. American Society of Plumbing Engineers, International Association of Plumbing and Mechanical Officials, International Code Council and American Rainwater Catchment Systems Association are among the organizations currently drafting such regulations. Reproduced below is a portion of an ICC news release published November 27, 2012.

" ...ICC is continuing to move forward with resources that will facilitate expanded application of rainwater harvesting systems, and ensure the preservation of health and safety while saving water. ICC Standard 805 will apply to the design, installation and maintenance of rainwater collection systems intended to collect, store, treat, distribute and utilize rainwater for potable and non-potable applications...Rainwater systems make use of a variety of unique devices such as first flush diverters, debris excluders and debris valves. At present no standards exist in the United States for these devices."

If rainwater collection is to become a widespread practice in Texas the writing is being scribbled on the wall: there will be more regulation and almost certainly requirements for treating cistern water when it's to be a source of potable water and connected to public water supplies. Sounds like an opportunity for licensed water treatment specialists.

Turbidity and treatment

A careful look at Table 1 shows both higher turbidity in rainwater than recommended for effective UV treatment and lower pH, indicating relatively acidic water. As a licensed water treatment specialist you know high turbidity generally means low UV transmittance and poor UV performance. Low pH water can lead to metal thinning and pipe corrosion.

Suppliers of UV equipment generally recommend testing cistern rainwater for the following contaminants - the maximum value of each is shown:

  • Hardness: less than 7 grains
  • Iron: less than 0.3 ppm
  • Manganese: less than 0.5 ppm
  • Tannins: less than 0.1 ppm
  • Turbidity: less than 1 NTU
  • UV transmittance: 75% is "minimum"; higher than 75% is "better"

If your cistern water quality doesn't meet these standards, it's been our experience designing and installing rainwater collection systems that various gutter screen and first-flush diverter products can significantly reduce tannin, turbidity and UV transmittance in cistern water. We have never seen hardness, iron or manganese in field or lab reports near, at or above the maximum values shown above.

What to do about low pH?

pH levels between 5.5 and 6 can be raised to 7 by installing a backwashing filter. An acid neutralizer is an “easy and effective way to raise the pH of acid water” according to Water Right University study materials. The company recommends using only the following media combinations: 100% Calcite media on a pH above 6; a mixture of 80% Calcite and 20% Corosex for pH between 5.5 and 6 are available that can raise pH levels from under 6 to 7.  Depending on the application these solutions can increase hardness by as much as 8 grains.

How can water treatment specialists improve the quality of rainwater?

The evidence seems clear – cistern-stored rainwater is a very high quality water. But if your customer wants to drink it, you must have it tested for contaminants. The most significant, in our experience, are listed below. If the value of any contaminant, particularly turbidity, tannins, UV transmittance, odor, taste and color are outside the limits shown below, install the appropriate pre-treatment devices. Test the water after installing the device(s). Add or reconfigure your pre-treatment installation until your test results show contaminant levels at or below the values shown below. Now you can size your UV equipment properly and add it to the system.

Think about it.

Look at what you can offer. Rainwater beats EPA standards virtually across-the-board. Cistern-stored rainwater samples have tested far superior to treated city water samples in major Central Texas metros and there’s no reason to think any metro area would be significantly “better” than those described. Your customer might need to install very affordable pre-treatment devices (approximately gutter foam at $4-5 per foot for gutter foam, $30-$75 for first flush diverters depending on diameter and $40 for Leaf Beaters) to reduce or eliminate contaminants that will allow UV equipment to function properly.  And if cistern pH is too low, recommend an acid neutralizing filter. Then look at what you have. Test the water – chances are high you have the best water on the block – probably the best water in the neighborhood. And it’s “green.” That looks like an opportunity for TWQA members.

Shaffer is co-founder of Texas Water Savers Co. (La Grange, Texas), TCEQ-licensed Class III Water Treatment specialist, staff member of The Rainharvest School staff member, Colorado River Watch Network volunteer, WaterCare dealer and TWQA member.


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