$re = '/Hagestein boven.+?(?:<td>Waterhoogte<\/td><td>)(.\d*)/';
$str = '>H10</td><td><a target="_blank" href = "http://www.rws.nl/images/GRAVBVN_tcm174-335817.pdf">meer</a></td></tr><tr><td><a href=\'awd.php?mode=html&projecttype=waterstanden&category=1&loc=GREB&net=LMW\'>Grebbe</a></td><td>21/04 17:30</td><td>Waterhoogte</td><td>643</td><td>cm NAP</td><td>LMW</td><td>GREB</td><td>H10</td><td></td></tr><tr><td><a href=\'awd.php?mode=html&projecttype=waterstanden&category=1&loc=GREV&net=LMW\'>Grevenbicht</a></td><td>21/04 17:30</td><td>Waterhoogte</td><td>2623</td><td>cm NAP</td><td>LMW</td><td>GREV</td><td>H10</td><td><a target="_blank" href = "http://www.rws.nl/images/GREVBT_tcm174-335691.pdf">meer</a></td></tr><tr><td><a href=\'awd.php?mode=html&projecttype=waterstanden&category=1&loc=GRPO&net=LMW\'>Groene Riv Pannerden ben</a></td><td>21/04 17:30</td><td>Waterhoogte</td><td>1143</td><td>cm NAP</td><td>LMW</td><td>GRPO</td><td>H10</td><td></td></tr><tr><td><a href=\'awd.php?mode=html&projecttype=waterstanden&category=1&loc=GRPB&net=LMW\'>Groene Riv Pannerden bov</a></td><td>21/04 17:30</td><td>Waterhoogte</td><td>1153</td><td>cm NAP</td><td>LMW</td><td>GRPB</td><td>H10</td><td></td></tr><tr><td><a href=\'awd.php?mode=html&projecttype=waterstanden&category=1&loc=HAAN&net=LMW\'>Haandrik Kruisbrug</a></td><td>21/04 17:30</td><td>Waterhoogte</td><td>910</td><td>cm NAP</td><td>LMW</td><td>HAAN</td><td>H10</td><td></td></tr><tr><td><a href=\'awd.php?mode=html&projecttype=waterstanden&category=1&loc=HAGO&net=LMW\'>Hagestein beneden</a></td><td>21/04 17:30</td><td>Waterhoogte</td><td>98</td><td>cm NAP</td><td>LMW</td><td>HAGO</td><td>H10</td><td><a target="_blank" href = "http://www.rws.nl/images/HAGSBNDN_tcm174-335693.pdf">meer</a></td></tr><tr><td><a href=\'awd.php?mode=html&projecttype=waterstanden&category=1&loc=HAGB&net=LMW\'>Hagestein boven</a></td><td>21/04 17:30</td><td>Waterhoogte</td><td>272</td><td>cm NAP</td><td>LMW</td><td>HAGB</td><td>H10</td><td><a target="_blank" href = "http://www.rws.nl/images/HAGSBVN_tcm174-335697.pdf">meer</a></td></tr><tr><td><a href=\'awd.php?mode=html&projecttype=waterstanden&category=1&loc=HANS&net=LMW\'>Hansweert</a></td><td>21/04 17:30</td><td>Waterhoogte</td><td>180</td><td>cm NAP</td><td>LMW</td><td>HANS</td><td>H10</td><td><a target="_blank" href = "http://www.rws.nl/images/HANSWT_tcm174-335699.pdf">meer</a></td></tr><tr><td><a href=\'awd.php?mode=html&projecttype=waterstanden&category=1&loc=HAWIb&net=LMW\'>Hansweert wind (b)</a></td><td>21/04 17:30</td><td>Waterhoogte</td><td>179</td><td>cm NAP</td><td>LMW</td><td>HAWIb</td><td>H10</td><td></td></tr><tr><td><a href=\'awd.php?m';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php