NEW YORK, May 6 /PRNewswire/ -- Water Asset Management today mailed the
following letter to shareholders of Insituform Technologies, Inc. (Nasdaq:
INSU):



                     [WATER ASSET MANAGEMENT LETTERHEAD]

                  The Time for Change at Insituform is Now!

    May 6, 2008

    To Our Fellow Stockholders of
           Insituform Technologies, Inc.:
    With Insituform's Annual Meeting of Stockholders less than two weeks
away, we're encouraged by the positive response our message for Board
change is receiving. In order to increase shareholder value for the long
term, Insituform needs more than just a few new voices on its Board -- it
needs a completely new board.

    The Incumbent Board's Desperation is Showing

    Shareholders recognize the need for change, and Insituform's incumbent
Board is becoming more desperate. In the absence of a track record they can
defend, they've taken to repeating an unfounded and inaccurate mantra. The
incumbent Board continually claims that we "have no plan or relevant
capabilities to operate your Company" and that we are "seeking Board
control to pursue a fire sale of your Company." These inaccurate
misrepresentations are a thinly veiled "scare tactic" and are completely
untrue.



     * Under no circumstance will we pursue a "fire sale" of Insituform.  To
       say otherwise is outrageous.  We are long term investors, focused
       exclusively on water related companies worldwide, and we are not
       looking for a quick sale in order to satisfy some mythical short-term
       investment horizon that management would like you to believe we have.
     * Our nominees are uniquely equipped to maximize long term shareholder
       value by implementing the business plan we have detailed in previous
       filings.  In fact, our nominees have far more experience than the
       incumbent Board in implementing efficient business practices throughout
       a global organization and in operating and investing in the water
       industry worldwide.  Moreover, our nominees have far greater
       governmental and international experience and contacts than the
       incumbent directors.
     * We have consistently stated -- and reiterate -- that we are prepared
       and willing to work with Joe Burgess as Insituform's new CEO.  In fact,
       if he is not reelected to the Board as a result of this proxy contest,
       we will offer to add him back to the Board.

    The Incumbent Board has demonstrated no ability to create shareholder
value.

    In response to our recent criticism of the Board -- and criticism by
analysts and other shareholders -- pointing to a long term record of
destroying shareholder value, the incumbent Board recently presented its
latest version of a "strategic plan." We see few new specifics and many
inaccuracies.



     * Insituform's shares have lost 13.2% of their value over the past five
       years, while the Company's two handpicked indexes for comparison have
       increased in value by 391.7% and 224.0%, respectively.(1)
     * In Q1 2008, gross margin remained well below historical levels, and
       operating expenses were still greater than analyst expectations, even
       after accounting for proxy related expenses.
     * The incumbent Board references operations in "40 markets," including
       North America (2 countries) and Europe (perhaps 10 countries), which
       implies, based on the incumbent Board's recent presentation, that sales
       in "rest of world" (approximately 28 countries) totaled a paltry
       $2 million in 2007.
     * Tite Liner sales have barely grown in the last 3 years despite the
       unprecedented boom in mining and oil and gas spending.
     * The incumbent Board's "strategic plan" now uses words like "refocus"
       "intensify" "improve" "reduce" "optimize" and "standardize."  Ironic
       how those words were rarely ever used before our filings.
     * The Company belittles litigation with its European partner (in a joint
       venture that accounts for a significant portion of the Company's non-US
       revenue) by referring to it euphemistically as a "situation."
     * The incumbent Board's public presentation of its plan shows an EBITDA
       chart that generously excludes the losses under their watch from the
       now-defunct tunneling business, and includes interest income, gains on
       sale, and other income.
     * The incumbent Board has apparently rebuffed past inquiries by credible
       buyers, never exploring whether they would be willing to pay
       shareholders a significant premium.

    Our objective is to transform Insituform into a results-driven
enterprise, with individual accountability, in order to create shareholder
value. Our 2010 EPS objective is $2.00 per share, as compared with $0.47
per share earned in 2007. Here are the highlights of some of the steps we
will take:



     * Grow sales from $500 million to $700 million.
     * Increase gross margins from 18% to 25%.
     * Reduce general and administrative expenses by $10 million per year.

    We urge you to vote for our entire slate on our BLUE proxy card. We
look forward to continue speaking with many of our fellow shareholders in
advance of the 2008 Annual Meeting on May 19, 2008.

    In addition, please feel free to call our proxy advisors, MacKenzie
Partners, Inc., or us directly, at any time for further information at
(800) 322-2885.



     Very truly yours,

     Matthew J. Diserio                           Disque D. Deane Jr.


     (1) Represents total return for calendar years 2003 through 2007.  The
         Company's handpicked indexes are identified in the Company's Form
         10-K and in Water Asset Management's proxy statement, filed March 10,
         2008 and April 22, 2008, respectively, with the Securities and
         Exchange Commission.


                         Biographies of Our Nominees

     * Nickolas W. Vande Steeg is a former President of Parker-Hannifin Corp.,
       having held a variety of executive and operating management positions
       over a 35 year career with that company.  Parker Hannifin is widely
       considered one of the best managed and most efficient companies in the
       S&P 500.  Mr. Vande Steeg has substantial experience in successfully
       implementing "lean" business practices in a large global enterprise and
       will provide significant leadership and insight to make the Company
       more efficient, flexible and competitive.

     * Senator Alfonse M. D'Amato offers a wealth of experience in
       governmental and international affairs on the federal, state and
       municipal levels.  Municipal wastewater markets are the primary focus
       of the Company's US marketing efforts for rehabilitation projects, and
       we believe Senator D'Amato's experience, insight, and relationships
       will be invaluable.

     * Matthew J. Diserio and Disque D. Deane Jr. are President and Chief
       Investment Officer, respectively, of Water Asset Management, which
       invests exclusively in water-related companies globally.  In addition
       to vast experience in the water industry, Messrs. Deane and Diserio
       will bring to the Board significant financial experience.  We believe
       their financial and water industry experience and contacts will be an
       important addition to the new Board's expertise in the current
       financial environment, where creative approaches to financing municipal
       projects can provide a critical competitive advantage.

     * Richard Onses is a water industry consultant based in Barcelona, Spain
       and specializing in water utilities and water infrastructure projects.
       He formerly headed business development at Sociedad General de Aguas de
       Barcelona, SA, a large European water company, and has operated water
       and waste water assets on three continents. Given the growth of the
       Company's international operations, we believe that Mr. Onses'
       international experience and contacts in the water industry will be a
       valuable addition to the Board.

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