Millers always needed enough water, even at the expense of the mills downstream. Between 1563 and 1568 this grew into a real ‘mill war’ between Diegem and Vilvoorde, in which religion also played a part. Henry de la Gruse, owner of the Hofmolen, was the leader of the Calvinists in the area, and the lord of Diegem, Karel van Brecht, was also on the Calvinist side. Opposite them stood the Catholic millers of Vilvoorde.
De la Gruse held back the water of the Woluwe at his mill, so that the Vilvoorde mills ran dry. In 1567 the tenants of the royal mills of Vilvoorde complained to the Chamber of Accounts in Brussels. The steward Frans van Dieve investigated, together with Aert de Bosschere, the ‘waterpreter’ who checked the water level in Diegem. The mill's tenant, Peeter Geerts, had tampered with the weir; he refused to change anything and said he was only following the orders of Karel van Brecht. The weir was repaired, with a fine of 20 gold reals threatened if it happened again, but De la Gruse simply had the mill set to suit himself once more.
After that Peeter Geerts and his son-in-law Willem de Cuestere, nicknamed Titau, took over the mill. They diverted the water so that it no longer flowed to Vilvoorde but straight to the Senne, by the old course of the Woluwe and the Hollebeek. When an extra beam of pear wood with a lock was fitted, they broke it away; they had evidently got hold of the key. The Vilvoorde millers wrote that in nine hours they could no longer grind as much as they used to in two. The case went to the Council of Brabant. We do not know how it ended, as the judgement has not survived. With the banishment of De la Gruse in 1568 the struggle stopped.
Later quarrels
There were still disputes later, but never as fierce. In 1640 Johan Jourdain, owner of the Broekmolen and secretary of the Council of Brabant, went to court over the water level; his opponents did not appear, and on 9 March 1641 he won his case. In 1766 Baroness de Piermans, lady of Diegem, sued the paper maker Jan Baptist Sebier for laying a pipe over the Hollebeek to bring water from a pond to his paper mill. Sebier had nevertheless paid 100 patacons to the Diegem authorities for it. The bailiff was given a festive welcome at his house, and after months of proceedings the baroness's petition was rejected on 6 July 1767.